new MAP sensor makes idle worse

[jdamron]

I have a 1998 Grand Am 2.4L with about 155,000 miles. The engine seems to run pretty smooth and has sufficient power when driving. However, at idle the engine sounds rough and seems like it is missing. The longer I idle the worse it gets. And if I am stuck at a traffic light long enough it will stall. There is not a check engine light on.

So, I put in new AC Delco plugs with the right gap and since then the engine runs much smoother, but still rough at idle. Then I tested the ignition coils and they seemed to be in range with a resistance of about 5.9 kiloohms for each one. I also cleaned out the ERG valve that did seem to be sticking. Next I changed the gas filter. However, the rough idle has not improved. And while poking around I noticed that if I unplugged the electrical connection to the manifold absolute pressure sensor that the idle actually improved, although this caused the check engine light to come on. I then tried to test the MAP sensor using the instructions in the Chilton manual. And the readings I received were all over the place. So just today I put in a brand new MAP sensor. However, with the new MAP sensor the idle seems to be even worse. In fact I could hardly run the car at all after a couple of minutes of idling. So, I unplugged the new sensor and the car sounds pretty good at idle except that now my check engine light is on.

Does anyone have any ideas? Could I have a short in the system somewhere, a bad computer, or is it something else related to the MAP sensor. Am I doing any damage by running the car with the MAP sensor disconnected? Any ideas would be appreciated. The car has lots of miles on it and I am trying to avoid taking it to the dealer if I can help it.

Thanks in advance.

[Matt95GT]

Does anyone have any ideas? Could I have a short in the system somewhere, a bad computer, or is it something else related to the MAP sensor. Am I doing any damage by running the car with the MAP sensor disconnected? Any ideas would be appreciated. The car has lots of miles on it and I am trying to avoid taking it to the dealer if I can help it.


Have you done any other troubleshooting? There are tons of other possibilities... vacuum leaks, IAC, O2 sensor, etc etc. Does it only idle poorly when warm? Cold? Both?

Yes, you will do damage running no MAP sensor. The MAP sensor is absolutely required to calculate the amount of fuel to be injected for the 2.4 (speed-density system). Without it, the PCM has no clue how much fuel needed... it just dumps in fuel for the purpose of getting you home.

[jdamron]

Have you done any other troubleshooting? There are tons of other possibilities... vacuum leaks, IAC, O2 sensor, etc etc. Does it only idle poorly when warm? Cold? Both?

The only cracked/broken vacuum hose I found was the short one that connects directly to the MAP sensor. And I just replaced that hose along with the MAP sensor. And I have checked all the other hoses for vacuum leaks, but I have not found any more. I have not actually tested the vacuum or the other sensors, but I do not have any codes in the system. Is it possible that the o2 sensor or some other emission control component is bad and yet does not register on the computer with a code?

It does seem to be a little worse when the engine is warm than when it is cold -- but not by much. It pretty much starts to idle rough after about 30 seconds of starting it up. And it just seems like the longer it is idling the worse it gets. But as long as the car is not stopped it actually sounds pretty good.

I guess I should try to test the other components next. I think the problem has something to do with the emission control system. Thanks for the ideas.

[spy]

check the o2 sensor, check the IAC sensor, and yeah again go over the motor looking for leaks.

[jdamron]

I did some more testing today using the instructions in the Chilton manual.

-- If I test between terminals A and C with the key on and engine off I receive 5.03 volts, which is in the expected range.
-- If I test between terminal B and A with the key on and the engine off I receive 4.89 volts, which does not make since because Chilton says I should get about .5 volts.
-- If I test between terminals A and C with the engine running I still get 5.03 volts.
-- If I test between terminal B and A with the engine running at idle I get 2.3 volts. And if I increase the throttle I get about 1.7 volts.

And now the computer is setting code P0107. Chilton lists the following possible causes for P0107:
* MAP sensor signal circuit shorted to sensor or chassis ground
* MAP sensor power circuit open between the sensor and PCM
* MAP sensor is damaged or has failed
* PCM has failed

Based on my voltage test and the fact that this is a new sensor does anyone have any suggestions on wrong might be wrong. I am wondering if I damaged the electrical connections to the MAP sensor by testing and replacing and again testing the sensor.

Thanks.

[spy]

I did some more testing today using the instructions in the Chilton manual.

-- If I test between terminals A and C with the key on and engine off I receive 5.03 volts, which is in the expected range.
-- If I test between terminal B and A with the key on and the engine off I receive 4.89 volts, which does not make since because Chilton says I should get about .5 volts.
-- If I test between terminals A and C with the engine running I still get 5.03 volts.
-- If I test between terminal B and A with the engine running at idle I get 2.3 volts. And if I increase the throttle I get about 1.7 volts.

And now the computer is setting code P0107. Chilton lists the following possible causes for P0107:
* MAP sensor signal circuit shorted to sensor or chassis ground
* MAP sensor power circuit open between the sensor and PCM
* MAP sensor is damaged or has failed
* PCM has failed

Based on my voltage test and the fact that this is a new sensor does anyone have any suggestions on wrong might be wrong. I am wondering if I damaged the electrical connections to the MAP sensor by testing and replacing and again testing the sensor.

Thanks.


You shouldn't have it damaged. I don't see how, it would be damaged. Are you sure you have the sensor hooked up to the proper nipple on the throttle body?

[98se]

make sure that the hose isn't collapsing when it gets hot.

[jdamron]

You shouldn't have it damaged. I don't see how, it would be damaged. Are you sure you have the sensor hooked up to the proper nipple on the throttle body?

Yes, there is really only one vacuum nipple on the throttle body that fits the small hose that connects to the MAP sensor on this engine. I ordered the original GM part of the small hose because it has a severe curve and the generic vacuum hoses tended to kink. Here are a couple of pictures. Thanks for asking though. I just thought maybe by back probing the electrical connections during testing that somehow I created a short.

[spy]

wait a minute... sorry the vacuum if i remember for the map sensor..

teh vacuum source is on a lil nipple just below the throttle body. all the vacuum crap on the throttle body go as such. One hose goes to the fuel pressure regulator, I believe two of them are emissions related, and one is the brake booster, plus the IAC and TPS. Then below the throttle body there should be another nipple for the map sensor so it's getting vacuum directly from the intake manifold.

Do yourself a favor and make sure that nipple isn't clogged up with gunk or anything. Check with a sewing needle or something pointy.

[jdamron]

Today I tested the Idle Air Control Valve as suggested. And I could not read any resistance at all -- it seems like there was a complete short in my Idle Air control Valve. So, I installed a new Idle Air Control Valve ($79). The good news is that the check engine light is now off and all the sensors appear to be working again -- I am no longer running in the default computer loop mode. I drove around for a few minutes and the light did not come back on so far. The bad news is that the engine is still pretty rough at idle. It might be my imagination but it does seem to be a little bit better than before, but it is still rough at idle. I am going to try to just drive it for several days and see what happens.

Also, I noticed that it seems like when it idles a while after just starting up that I get some water out of the back tail pipe and muffler. I am wondering if I have some type of internal water leak and that might be the real source of my rough idling. Does anyone have any suggestions on how to tell for sure if I have an internal water leak and how to figure out where it is?

Thanks.

[spy]

Today I tested the Idle Air Control Valve as suggested. And I could not read any resistance at all -- it seems like there was a complete short in my Idle Air control Valve. So, I installed a new Idle Air Control Valve ($79). The good news is that the check engine light is now off and all the sensors appear to be working again -- I am no longer running in the default computer loop mode. I drove around for a few minutes and the light did not come back on so far. The bad news is that the engine is still pretty rough at idle. It might be my imagination but it does seem to be a little bit better than before, but it is still rough at idle. I am going to try to just drive it for several days and see what happens.

Also, I noticed that it seems like when it idles a while after just starting up that I get some water out of the back tail pipe and muffler. I am wondering if I have some type of internal water leak and that might be the real source of my rough idling. Does anyone have any suggestions on how to tell for sure if I have an internal water leak and how to figure out where it is?

Thanks.

In the morning it is just simple condensation from the humidity in your area where you live in. Don't worry about it.

If the car is idling a bit rough or seems to be "missing". You can always check your spark plugs to see if they're in need of replacing. Another thing, is that if your car has higher mileage it may be worth it to have your injectors cleaned and balanced. That is if you intend to keep the car for a long while. www.rceng.com can perform this service as I wouldn't exactly trust the everyday shop where all they'd do is dump some additive into your gas tank. Also you can have your coils checked out to see if they're starting to slowly lose their "pep".... i said pep.. hehe.

[jdamron]

In the morning it is just simple condensation from the humidity in your area where you live in. Don't worry about it.

If the car is idling a bit rough or seems to be "missing". You can always check your spark plugs to see if they're in need of replacing. Another thing, is that if your car has higher mileage it may be worth it to have your injectors cleaned and balanced. That is if you intend to keep the car for a long while. www.rceng.com can perform this service as I wouldn't exactly trust the everyday shop where all they'd do is dump some additive into your gas tank. Also you can have your coils checked out to see if they're starting to slowly lose their "pep".... i said pep.. hehe.

Thanks spy for the additional ideas.

Yes, I understand now that I am probably just seeing normal condensation in the morning around the tailpipe.

I did just a few weeks ago replace the spark plugs with AC Delco plugs with the right gap. And I also tested the coils at the same time. I have also added some additives myself to the fuel tank -- SeaFoam.

I drove the car this morning about 30 minutes to work and I no longer have any check engine light. However, it is still rough at idle, especially after the car warms up. Thanks for the idea of the mail order fuel injector service -- I might give that a try.

[spy]

The only other real thing that would and could case the car to run funky at idle would be the Coolant Temp Sensor, o2 sensor, or maybe the ICM module. That come to mind.

OH! Check with a simple volt meter or gauge how many volts your motor is up at. I know that after making sure and beefing up my grounds around the car, I did get smoother operation.

[jdamron]

Well, since my last post I have replaced a few more parts and done some additional work, but unfortunately I still have my rough idle problem. I have now replaced the Idle Air Control Valve, replaced the Fuel Pressure Regulator, replaced the O2 sensor, and cleaned the Throttle Body since my last post.

So I took it to the dealer for diagnostics because I was running out of things to try. And the dealer could not find any issues when using their computer equipment and recommended I get another car. So, I called a local mechanic shop and they suggested I might possibly have a leaking intake manifold gasket. I had told them that it seems to run find under normal driving, but then after idling a little while it runs really rough and the whole car starts to shake. It seems to be worse the longer I idle. And I am loosing a few ounces of coolant each week. I do not see any water leaks, and the local shop thinks possibly coolant is entering the chamber and causing it to run rough.

So, it looks like a pretty large job to replace the intake manifold gasket, so I thought I would check here to see what you guys think. I do seem to have quite a bit of oil leaks, but I cannot tell that the intake manifold is leaking. I have attached below some pictures. The most prominent leaking I could find is around the spark plugs.

Do you think I should replace the intake manifold gasket next?

[jdamron]

Here are some more pictures.

[jdamron]

And some more pictures.

[Matt95GT]

Both your dealer and mechanic sound like they don't know what the hell they're talking about. "Get a new car"... not even gonna comment on that incompetence. Hope they didn't charge for that advice.

The intake manifold gasket leak doesn't affect the 2.4... that's a problem on the V6's only. The intake gasket on the 2.4 cannot possibly leak any fluids.

I would still suspect ignition system components... they are the biggest culprit for 2.3/2.4's that run rough.

[spy]

the ignition components like matt just said.

and also you're saying you are losing coolant? are you sure there are no visible coolant leaks anywhere? you might have a headgasket leak. When driving under power you're burning it off sufficiently, but at idle it's not burning off fast enough.

Does your exhaust smoke a lil at idle?

[jdamron]

Thanks Matt and Spy for the ideas. The good news is that the dealer did not charge me anything for the diagnostics since they could not find the problem. And I got the impression they just wanted to sell me a new car, so I definitely need to take it somewhere else. The mechanic shop I called is really busy and can not look at it until next week and was just giving me some ideas over the phone about what the problem might be. Your feedback about the LIM problem makes since because I could not find any input to the intake manifold on my car other that 'air'.

Yes, I am loosing just a few onces of coolant a week. And it does look a little wet around the engine. It is hard to tell in the photos I uploaded. And I am not sure how much of the wetness I am seeing is oil or coolant. And I just really do not see any exhaust smoke at idle. If there is any it is very faint. But the idle is very rough -- you can feel the whole car vibrate and the air intake hose looks like an accordion!

Thanks,

Jonathan

[Ralph]

unless your manually throwing coolant into your throttle body there is nothing but air they probably just heard grand am and assumed that without even looking at it. Probably is the ignition giving you all these problems both of mine have acted up before.

[jdamron]

Well, this afternoon I went ahead and took off the throttle body so that I could clean it thoroughly. There was a lot of gunk and I was thinking that perhaps some of the vacuum lines going out of the throttle body might have been clogged. I have attached before and after pictures.

Not surprising I still have the same problem. Here is a little more detail on the exact symptoms. If I run the car under normal driving conditions the engine sounds great to me. And after driving it for a few minutes and coming to a dead stop and idling for several seconds it sounds fine. But after idling for about 10 to 15 seconds it starts to sound like the engine is missing and the engine shakes a lot. And then the longer I idle the worse it gets. If I let it idle for several minutes without giving it any gas it will generate a P0300 (multiple random engine misfire) code. But if I reset the code and give it some gas it sounds just fine. But as soon as I let up on the gas and let it idle it sounds rough again. It looks like it normally idles at around 800 to 900 RPS. As soon as it has just a little bit of gas and the RPMs are around 1000 or 1100 RPMs it sounds smooth.

The consensus of the replies I have received on this thread seem to suggest I have an ignition problem. I have replaced the spark plugs with AC Delco parts at the right gap, replaced the spark plug boots, and tested the ignition coils. I would be greatful if you have any specific ignition components I should test or replace next.

Thanks in advance.

[Vampyrate]

if you are losing coolant, check the water pump (though i still dont understand why they call it a water pump when it actually pumps coolant these days)

as for the idle, i would replace the wires and maybe the ground wires as well... you can make a ground wire kit out of 0ga audio wire and have plenty left for other projects. i think the stock wires are like 2ga or something, so that may help. other than that, i would look at the pistons and see if there is any warping of the pistons or damage to the cylinder walls.

[jdamron]

Thanks Vampyrate for the ideas.

if you are losing coolant, check the water pump (though i still dont understand why they call it a water pump when it actually pumps coolant these days)

I actually did replace the water pump a few months ago (http://www.gaownersclub.com/forum/showpost.php?p=1123265&postcount=9), and I do not see any visible water leaks. Right now I am only loosing a few ounces a week.


as for the idle, i would replace the wires and maybe the ground wires as well... you can make a ground wire kit out of 0ga audio wire and have plenty left for other projects. i think the stock wires are like 2ga or something, so that may help. other than that, i would look at the pistons and see if there is any warping of the pistons or damage to the cylinder walls.

I would definitely replace wires except that my particular engine does not have any. I have the integrated ignition control module that sits right on top of the spark plugs without any external spark plug wires wires. I wonder if there is a way to test the integrated control module? I hate to replace it without knowing it is bad because it just looks like a big plastic box with some contact points, so I am not sure what could go wrong in there.

Thanks.

[Ralph]

There is a testing procedure for it I just have to look through my manual im sure someone will post it before I find it. The coilpack which is that white housing is almost always the problem. The "wires" are actually those back boots with the springs in them.

[jdamron]

So here in an update. I took my car to a local mechanic shop that is well known and respected in this area. I paid them $84.50 for a diagnostic. They said my exhaust was rich and the engine was misfiring. They recommended replacing the spark plugs, spark plug boots, both coils, coil housing, and the ignition control module. I was hoping they could narrow down the problem more than that but at least they agreed with the consensus of this thread that I have some type of ignition problem. They also said my battery was weak. They wanted $750 to fix.

I had already replaced the plugs and boots and tested the coils about two months ago. However, the shop said that coil resistance testing is not always enough because when the coils heat up they can still have problems even when they pass resistance testing.

So, the first thing I did is I replaced both coils -- and the results were exactly the same.

Then I put in a new ignition coil housing -- and the results were exactly the same.

Then today I put in a new ignition control module ($140 yikes!). However, the car now sounds a lot different with the new ignition control module. It seems to run faster with shorter time between misfires if that is possible. The engine seems to vibrate faster than before. And now I get a P0301 code every time I run it after just a couple of minutes whereas before I would only get a p0300 once in a while after idling for a very long time. And now I can feel sluggishness when accelerating, which is something I did not notice before. And in addition, the engine light is flashing along with the new P0301 code which it never did before. So, it is almost like the problem is worse and/or different with the new ignition control module.

So, one of the possible causes of P0301 I found in my manual is a bad fuel injector. In order to check this I just finished switching my #1 and #4 fuel injectors. I was hoping to get a P0304 if the problem was the fuel injector. However, I just finished test driving it and I still have P0301 after the fuel injector switch.

So at this point I am about ready to give up. I have recently (over the past three months) replaced all of the following:
- water pump, timing chain, & water outlet (not related to rough idle problem but because of coolant leak)
- spark plugs
- spark plug boots
- cleaned ERG valve (did not replace)
- MAP sensor and short vacuum hose to this part
- throttle position sensor
- fuel filter
- idle air control valve
- fuel pressure regulator
- o2 sensor
- both coils
- coil housing
- ignition control module

And now I have a flashing P0301 and problems worse than when I started.

Does anyone have any suggestions before I call it a loss and give up?

Thanks in advance.

[jdamron]

Okay, so here is yet another update. It turns out that the reason my car sounded worse and had a P0301 with the new ignition control module was due to user error. This afternoon I took off the ignition module housing again from off the top of the spark plugs and noticed while doing so that I had not perfectly aligned all four spark plug connectors. So it turned out that there was not a good alignment of the housing to the spark plug boot for my #1. Oops! I put it back together being careful to have everything aligned correctly and now I no longer have P0301 with the new ignition control module.

I am now basically back to square one. The idle is now no better or no worse with all the new ignition parts. But at least it is not worse! At this point I am at a loss as to what the real problem is. I have replaced all the ignition components and several other sensors and parts as explained in this thread and the rough idle problem is the same as when I first started. If anyone has any other ideas I would be very interested in hearing them.

Thanks,

Jonathan

[Pontiac]

Long shot, did you test that a spark was flowing to the appropriate plugs?
Longer shot, theres not a potato stuck in the exhaust pipe, is there?
Longest shot possible, but did you do a compression test?

The compression test I have a feeling I'll get flamed for, but, my reasoning for that is that maybe you've got a large enough leak and the piston isn't being pushed as hard as it should be, there by throwing the whole rhythm of the engine off. Although, you would be seeing a lot of other issues such as blue smoke out the pipe... unless that potato isn't letting any smoke out to begin with. {smirk}

[jdamron]

Thanks Pontiac for the additional ideas. I do not see anything stuck in the exhaust pipe, but I have wondered if perhaps my exhaust is partially clogged for some reason. I have not done a compression test.

Yesterday I picked up a fuel and vacuum test kit from Harbor Freight Tools. I tried taking readings with the car idling from two different places, but I could not get any reading at all. I do not have a PCV hose. So, I tried placing the gauge (using the 'T') between both the MAP sensor and the intake manifold and also between the fuel pressure regulator and the throttle body. In both places I can feel suction with my thumb. But the vacuum gauge does not have any reading. Does it sound like I am testing this wrong? Or is it possible for me to have so severe a vacuum leak that it does not register? Perhaps this is my problem.

Thanks,

Jonathan

[Shadow-D]

only thing that makes sense to me might be a partly plugged cat but I'm not sure.

[jdamron]

It turned out that the first vacuum gauge I purchases was defective. I retested with a another gauge and now I can get a reading. The reading basically shows fast, jumpy fluctuation between 13 and 15 inches. I have uploaded a few short videos that illustrate the rough idle and the vacuum readings in case anyone would care to take a look. It is probably easier to understand what I am looking at by seeing it.

http://damronplanet.com/waterpump/roughidle.html

Thanks.

[Shadow-D]

:???:

[jdamron]

Based on some feedback I have received and what I could observe I was thinking I might have a leak in the intake gasket. So, I just removed the intake manifold. The gasket itself does not actually look that bad. Of course I will put in a new one. However, I did notice a lot of deposits inside the intake manifold. Does anyone have any suggestions for the best way to clean the intake manifold? It looks like it is made of a plastic like material and I am not sure if carborator cleaner will hurt it or not. Also, there are a lot of carbon deposits just inside the engine itself. Are there any tricks to removing those deposits without knocking things down into the valves. One last question -- it looks to me like one of my valves is burned. Do you think it is possible that that might be the root cause of my rough idle problems? I have uploaded some new pictures at the following URL in case anyone wants to look at them and see what they think about the valve in question.

http://damronplanet.com/intakemanifold/index.html

Thanks,

Jonathan

[bobtnt3]

Jonathan,

I am very interested in any developments with your car. I have a 2000 2.4l w/140k having exactly same problems down to the small coolant loss. Car runs great, doesn't idle worth a $%&^@.

[98NTc]

still need help idamron?

[whisla13]

Just bought a 1999 Grand Am with this EXACT problem. Figured it would be an easy fix, but I'm stuck. Anyone figure out anything?

Thanks,
Andrew

[DM77]

I essentially have the same problem with my 3.4 1999 Grand Am with 152000 miles. The problems I am have been having started with the replacement of the spark plugs with another type (Before replacing the plugs the car was running) I have been told and have read that the ignition in the Grand Am will accept nothing other than the ac delco plugs. Recently I have replaced the plugs with ac delcos, replaced the wires, changed the fuel pump, fuel filter and the fuel regulator. I have checked the resistance in the coils, and other controls. Have checked the voltage from the crankshaft pickup and all have tested good. I have pulled the upper intake and checked the injectors, replaced the gaskets and cleaned the throttle valve with carb cleaner. As of right now the car will not start. I have checked for codes, but there was none. I have been told that the map sensor could be bad. Waiting on more input

[Shadow-D]

I essentially have the same problem with my 3.4 1999 Grand Am with 152000 miles. The problems I am have been having started with the replacement of the spark plugs with another type (Before replacing the plugs the car was running) I have been told and have read that the ignition in the Grand Am will accept nothing other than the ac delco plugs. Recently I have replaced the plugs with ac delcos, replaced the wires, changed the fuel pump, fuel filter and the fuel regulator. I have checked the resistance in the coils, and other controls. Have checked the voltage from the crankshaft pickup and all have tested good. I have pulled the upper intake and checked the injectors, replaced the gaskets and cleaned the throttle valve with carb cleaner. As of right now the car will not start. I have checked for codes, but there was none. I have been told that the map sensor could be bad. Waiting on more input
Just to give you a heads up... This is the 2.4 TwinCam I-4 section. Your problem with the 3400 3.4 V6 might be a different ball of wax. Try posting your question in THIS SECTION (http://www.gaownersclub.com/forum/forumdisplay.php?f=6).