Idling/Misfiring Problems

[RaptorRed67]

Greetings all,
I've found similar threads with problems similar to mine but none of them seem resolved or close enough to what I'm experiencing to help me. First off, '03 GAGT1 with the 3400 V6. Very mild engine mods so far: K&N cone filter replacing the intake track up to the MAF, slightly larger piping from the cat back to a Flowmaster 80 series muffler, MSD coils, Taylor s/p wires, Bosch platinum plugs. Not much else done to the engine yet, mostly just suspension mods. Don't worry I've got plenty planned down the road. I'm fairly good with cars and my knowledge is growing every day but there are some cases such as this where my experience with them just isn't extensive enough to help me figure it out myself.

So here's the issue. Just after a cold start (after sitting over night, after a day at work, etc) particularly when the weather is below about 45 degrees; the car sputters and misfires and idles rough. Sometimes it throws a code, sometimes not. Sometimes (most of the time) it just reads "Random/Multiple Misfire". Occasionally it will throw a specific cylinder, sometimes 4, sometimes 2, most often 3. Once I get it on the road and above about 1400-1600 RPM it smooths out and runs great. No hesitation, no bucking, nothing. In the past once it warms up (180-220 degrees) the sputtering doesn't come back when I bring it back down to idle at a light or stop sign, but now it is. It's been a brutally cold winter here in Ohio and now ANY time it's at idle it misses and runs rough, engine cold or hot.

Now then, let me make clear that this problem happened BEFORE I changed the coils, plugs, or wires. Along with a good upgrade, those items were changed in order to try and fix it. Didn't help but it seems to be becoming more prominent. I've double and triple checked all the connections and they seem to check out. Even the plugs are clean and the burn pattern on them looks fine. I've also replaced the IAC and the PCV valve to try and alleviate it. Next on the list is the TPS and MAP sensors but before I got into that I wanted to pick your collective brains to see if anyone else has come across this.

I have an AutoXray and throw it on whenever this happens to check the codes and to monitor whats going on when it's missing. Just about all the stats seem normal other than the fact that the fuel trims bounce around a bit (this seems to be normal at idle because it fluctuates slightly even when its idling fine) and my vacuum drops to about 9 psi. I have been told that this is symptomatic of the missing, not the cause. It holds a nice steady 16-17 psi once its up to speed so it's not leaking AT THAT RPM. I don't know about otherwise, checking the vacuum hoses and such is also on the list.

Alright I think that's all the info I can think to include for now. If I'm not being specific enough just lemme know. Is something like this common to the 3400s or GAs in general? Have other experienced this? Any help that you folks can offer would be greatly appreciated. I've been pooling all possible resources to try and find the solution for this sumb*tch, both here at work and on the web and so far no one seems to know for sure what it is. Thanks again all, I'm grateful.

[SE2000]

I would tend to look at things that sense a cold engine. The signal is either not getting through or the puter is ignoring them. Coolant, o2 and such. Did the problem occur after the K & N? Maybe it's the air intake sensor

[rixGAphx]

I'm not reading all that. :roll:

[RaptorRed67]

SE2000 -- Thanks, yes I've thought about it being the filter but wouldn't it do it all the time then, not just in cold weather? The IAC is also on the list of things to check. Thanks again.

rixGAphx -- Well congrats, whadda you want a cookie? If you didn't feel like reading the whole thing why reply to say that you don't want to. Just don't.

[rixGAphx]

:Cliff's Notes:
Symptoms point strongly to a vac leak; check the non-emissions vac system.Originally posted by RaptorRed67
rixGAphx -- Well congrats, whadda you want? :Cliff's Notes:
Engine idles erratically; used to do it only when cold, now does it even when warm.
Coils, plugs, and wires have been replaced; problem remained and now is worse.

"Sometimes it throws a code, sometimes not. Sometimes (most of the time) it just reads "Random/Multiple Misfire". Occasionally it will throw a specific cylinder, sometimes 4, sometimes 2, most often 3.
Once I get it on the road and above about 1400-1600 RPM it smooths out and runs great. No hesitation, no bucking, nothing. In the past once it warms up (180-220 degrees) the sputtering doesn't come back when I bring it back down to idle at a light or stop sign, but now it is."

Vaccum measures low (9 psi) at idle but haven't checked for vac leaks yet because, "I have been told that this is symptomatic of the missing, not the cause."
* * *

Could well be the Inlet Air Temp (IAT) sensor that SE2000 mentioned; if the 'puter doesn't know the actual temperature of the air, it can't correctly calculate the density and thus the amount of fuel to inject.
Once the engine warms, the PCM starts measuring the O2 in the exhaust and re-maps the fuel injection accordingly.

Might also be that installation of the filter inadvertently separated the vac tubing where it crosses the engine bay from block to vac reservoir.

Low vac at idle *might* be caused by the misfire/stumbling, but IMO that would be rare, mebbe 10% of the time.
More likely a vac leak is CAUSING the symptom.
I think somebody gave you a bum stear on that one.

IMO 70% of 'rough running/erratic idle' is caused by a vac leak:

1. Check the tubing, devices, and connections of the non-emissions vacuum systems for leaks:
* HVAC control, including the vac reservoir under the battery.
* Brake booster.
* Fuel Pressure Regulator.

2. I've seen a couple cases of rough idle/misfire (tho not on a GA V6) where the throttle plate wasn't closing fully (in one case, a twig was stuck between the plate and the TB :eek: ).
The effect is the same as a vac leak, but inspection of the vac system didn't reveal the obstruction.
The only measurable symptom was the low vac measurement.

3. The FPR might be faulty (or the vac line to it), causing too-rich a mixture.
This will not throw codes, so it might be the culprit.
Check it with the vac tester: it should hold vac, not leak-down.

* * *
The emissions (vapor recovery) portion of the 'vac' is very well-monitored by the PCM, and would throw specific codes.
So that system isn't at fault.

A problem with the Idle Air Control (IAC) valve might cause similar symptoms, but the IAC is also well-monitored and would most likely throw a specific code.
So it's prolly not that system, either.

IM experience, a partially-clogged fuel filter is much more noticeable at higher rpm, not low rpm/idle.
So that's prolly not the culprit.

A dirty/blocked air filter or partially-clogged cat are more noticeable at lower intake/exhaust flows of idle than at higher rpms (the higher pressures of high rpm's 'mask' the problem).
Though either of these can cause rough idling, they likely wouldn't cause an actual 'misfire' that would register as a code.

Good luck,
-Rick

[00SilverGA]

I am not looking to start a fight or anything but Rick is a wealth of knowledge and to be honest I am surprised he even responded to you after what you said. I know you are a newbie but In the future I suggest you be a little more respectful and probably keep your comments to yourself.

[RaptorRed67]

I stand humbly corrected, Rick, thank you for reading thru my post and helping. I honestly do appreciate it, someone with your kind of knowledge is exactly what I was hoping for.

As I mentioned before the air temp. sensor is on the list of things to replace to see if it helps, so I'm keeping my fingers crossed on that one.

You mention the vac tubing being seperated with the filter install. From what I can tell the vac tubing dumps back into the intake tube AFTER (engine side) of the MAF, unless what I'm seeing isn't a vac tube. It's a tube probably about .5 inches in diameter with a 90 degree elbow and press fitting that slides into a nipple on the tubing. There appears to be no change if I pull it out or place my finger over it. When I remove my finger there's a whoosing, sucking sound that dies down after a second or two. I'm guessing that is normal? Anyways, the air filter is before the MAF and that tube is still installed, is that the one you are referring to or is there another I should check for?

The TB is clear and clean, I checked that one early on in the symptoms as well as checking and cleaning the MAF. Both appeared fine.

You mention the fuel filter as well and I forgot to mention in my original post that I changed it last year as an effort to fix this. No good. Filter has also been thoroughly cleaned and re-oiled with care taken not to over oil it since this can cause problems if it gets on the MAF. I originally thought that might be the culprit as well but its clean.

This weekend is going to be a frozen thrash to try and test as much as possible before I have to drive for work again next week. Hopefully I'll end up netting some kind of result. Thanks again Rick and anyone else who throws in their 2 cents in the future, I am grateful.

--Dave

[SE2000]

The colder the weather, the more pronounced temp related things appear. Plus an engine thats only been off a few hours is still warmed up, fitting your symptoms.

[rixGAphx]

Originally posted by RaptorRed67
...thank you for reading thru my post and helping.
I honestly do appreciate it, someone with your kind of knowledge is exactly what I was hoping for.My pleasure.

Compliments not necessary.
(But greatly appreciated :D :D Thanks! ).


You mention the vac tubing being seperated with the filter install.
From what I can tell the vac tubing dumps back into the intake tube AFTER (engine side) of the MAF, unless what I'm seeing isn't a vac tube. ...is that the one you are referring to or is there another I should check for? Whatever you're toalking about (and I don't know, since I can't recall how a 3.4 is plumbed for air on the intake) isn't what I was referring to.

Look at the engine.
* To the top rear of the Upper Intake Manifold (UIM), at the left (as you face it from the bumper) is attached a 5/8 or 3/4" black rubber hose, and it goes to the Brake Booster, providing vacuum for the power brakes.

* About in the middle IIRC of the UIM, there's a smaller nipple with about a 3/8" diameter short black rubber nipple that receives a small-diameter plastic vacuum tube.
This is the source of the vac power to open and close little damper doors in the HVAC ductwork, for control of hot and cold air distribution.
* But this plastic tube doesn't go directly to the HVAC control panel on the dash.
Rather, it enters the wiring loom and snakes back, right, down, and forward of the engine (at least this is the routing on the 3.1, and yours is prolly similar).
When it comes to the lower front driverside of the engine, it is just above the tranny.

There's about an 8" open space (below the upper radiator hose) that the tubing must cross from the engine block to connect to the vacuum reservoir (black plastic ball about the size and shape of a grapefruit) under the battery.
There's a one-way valve and a 'Tee' nipple in the 'open space' before the tubing finally connects to the vac bottle.
It's kinda hard to see all this spaghetti under the rad hose, so peer closely with a flashlight.

All it takes is a dropped screwdriver or other minor accident while working on the driverside of the engine (like a filter install) to disconnect the 'Tee' from the vac bottle.
The HVAC controls will still operate most of the time, but there's no 'vacuum reserve' to operate them when vac drops very low for several minutes (like climbing a steep hill, almost 'flooring' the gas but still doing only moderate engine rpms).

* Of course, a similar tubing disconnect elsewhere could cause a big leak, but this little 'Tee' to the vac bottle is the only place the HVAC vacuum system can become disconnected yet still allow the controls to *mostly* work.

The 'Spray Test' with winter starting fluid is a quick and easy way to discover vac leaks; presuming you spray at all the possible leak locations.

Hope this helps,
-Rick

[rixGAphx]

Originally posted by 00SilverGA
...I am surprised he even responded to you after what you said. :lol:

I'm tougher than that.
Hell, I'M the one who started teh sarcasm.
It's cranky Friday. :D :D

I half-expected him to respond to MY post with, "I'm not reading all THAT!"

It's refreshing to hear from somebody with a tough skin.
Dave can come hang on some of the (milder) Jeep boards, but he's gotta bring his own flamesuit. :eek:

Peace, catch you all Monday.
-Rick

[RaptorRed67]

Many thousand thanks again Rick, now I have a plan of attack for tomorrow to try and hunt this mutha down. I hope, GOD I HOPE, I can find it. Its starting to get really rough.

My original post was a bit lengthy because I was trying to be as thorough as possible in describing the problem. The more you know the better you can help right?

Jeep boards ey? Rough crowd are they? I'll have to keep that in mind the next time I needa good hazing.

Thanks again mate. Cheers!

[RaptorRed67]

No news to report yet. I tried looking around to see what I could find to no avail. One of the main problems is, now that the weather temperature has gone up a bit it no longer idles rough. The temp ranges (weather temp.) that this happens in seem to be very specific, usually mid-to-high 20's and low-to-mid 40's will cause it while at all other temps its fine. ::sigh:: I'll keep trying and will update if I can come up with anything.