New update in 90 GA rough idle

[cage47]

So I'm finally getting some time to start my repairs. The first is the rough idle. I've changed the plugs and wires (two wires were arching and all plugs were gapped wrong). New oil. And complete engine diagnostic with no problems. No error codes, no vacuum leaks (had them check specifically) And fuel pressure is where it should be. I've run a tank of fuel with tbi cleaner and today put in the new fuel filter. Now it idles fairly smooth. BUT it still idles a little low. And it's not totally even. It sometimes revs down then back up. Slightly but noticeably. And the start takes a couple extra cranks to start still. Driving is still smooth. So I'm running out of things to check on this issue. I've heard of the fuel pressure regulator but don't think that's it. I'm wondering of an all out worn tbi. This is on the 4tech (not the quad). It's not enough to make a big concern but something I'd like to resolve eventually. But next on priority is the c/v joint and strut on the driver side.

[HeyDace]

That may be caused by Throttle bore coking and/or a defective IAC. Try cleaning the throttle bore. I'm not sure if the Haynes manual has the procedure to reset min Idle (curb idle), if it does, follow that.

[rixGAphx]

"I've heard of the fuel pressure regulator but I don't think that's it." ???

Well, your car is quite old, and this device is EXPECTED to eventually fail.
Unless you've just replaced the fuel pressure regulator, it IS a possible cause of the exact problems you describe.

A replacement should cost about $30 and take an hour.

I'm not necessarily saying throw money at possible solutions, but I think it's unwise to dismiss a likely culprit without evidence.

Good luck.
-Rick

[cage47]

ok here's the latest. I took it in to get the inspection. Didn't pass. Emissions. A test showed my egr valve was shot, the cat converter clogged and the intake manifold had a crack at the egr. So I went to pick a part got another intake, got a new egr and put them both in. Have to hold off on the converter, it needs the mounts put on. Anyway today driving in to work it's a mess now. I'm not sure what happened. At low rpms it bucks and jumps. And I now have a severe loss of power from yesterday before the repair. This is a big concern now because I fear this might interfere with the emissions test. I'm going to pull the tbi again to see if I misaligned the gasket. It now has the bad vacuum sucking sound I was hoping to avoid. But I replaced a bunch of bad lines already.

[cage47]

And another update. I drove home from work. Before leaving I unplugged the vacuum line from the pcv valve. Not because it was bad (it's actually new) but to test a theory. And sure enough. With that vaccuum line disconnected the engine reved right up. Even starting. It started right up. No cranking. And power was back. So I have it down to knowing it's running with either too much gas or not enough air. That comes down to the pressure regulator or the iac. Now the regulator is only $20 at oreillys but the IAC is $68. I now know it's nothing major because when the line was unplugged it ran smooth, no hesitation and no rough idle. So it's either a matter of getting more air in (iac) or less fuel in (pressure regulator). I'm leaning more to the iac but the regulator is a cheaper fix so I'll do that one first. But what other oppinions are there? Also where is the iac located and is there a way to test it. I can't find it in the Haynes manual.

[cage47]

OK You've gotta be kidding me! I mean it was a 50-50 shot which was bad. So last night I replaced the easy one. The fuel pressure regulator. That wasn't it. But it wasn't a bad idea to replace it. Once I got the old one out I could see the rubber diaphragm was wearing through. It would have given way soon. But my GOD! Twenty bucks for this stupid thing that's no bigger than a quarter. I thought it would at least include the spring. Nope just the rubber/metal diaphragm thing. Twenty bucks for THAT????!! I've got the IAC valve coming tonight. I've read up and see how common a problem that is. And this could also be why my emissions were so high. Running rich. I feel like I'm one step away from getting the Rocket in top notch running form again. And on the 31st I'm going to replace the shocks in the back and the bad strut and then it'll be in excellent shape all around. Though I do think I have to replace a brake piston in the back. But I can work with that for now.

[doobiess]

lol good luck on the IAC sounds like how my luck would do it. but hopefully that will fix your prob..

[cage47]

Nope. Now I'm running out of ideas. I've replaced the iac, the throttle position sensor, the fuel pressure regulator, the pcv valve and the egr valve. I know the egr valve was bad. And the fuel pressure regulator was going to give out. It was coming apart at the rubber. So that wasn't lost money. But the iac didn't help at all. It is the same, when I remove the vacuum line to let more air in it revs up and is smooth. So there is plenty air getting in since the iac is working. That leaves only the m.a.p. sensor. Or possibly the tbi injector itself. But I doubt that one. I'm going to find a map sensor at pick a part tomorrow. That has to be it. There's nothing left. Well aside from the ecm itself but I'm hoping to find it before that. See if it was a vacuum leak i would look for a vacuum leak. Since it would be getting too much air. That would be simple. But it's getting too much fuel. And that's an electrical control somewhere. And there isn't much left I haven't checked.

[cage47]

Oh rix. The pressure regulator cost $20 and it took me 5 minutes to replace. I hate the idea of throwing parts at it but electrical controls are a bugger to find problems in. But I'm down to the last items to check.

[cage47]

And Heydace. Is there a link anywhere here describing how to reset the curb idle?

[HeyDace]

I'm not sure, I don't believe it was ever discussed. But seeing its and older car, try this.

1. Start with a cold engine, turn the key on and wait about 45 sec. Then unplug the IAC (that seats the IAC)
2. Remove the tamper plug from the idle adjustment screw and back off the screw until it just touches the throttle linkage.
3. Hook a tach up and start the engine. (you may have to turn in the screw in 1/4 turn increments to get it to idle)
4. turn the screw in till you get to your desired curb idle.
5. Shut it down and reconnect the IAC, take it for a good run (40MPH or more for at least 5 min) That will relearn your new idle setting.

Back in the day the Idle reset was performed along with Throttle bore de-coking and It worked on my old '93 GP.

Hope that helps, good luck.

[cage47]

Alright here's the latest. Here is what I HAVE done.
New IAC
New TPS
New PVC Valve
New EGR Valve
Replaced intake manifold w/new gasket
Replaced MAP sensor with 3 used (no change)
replaced throttle body injector with 2 used (no change)
Even tried disconnecting the last sensor on the manifold right between the power steering pump and the tbi (no change)

BUT I tried disconnecting the O2 sensor. Progress. It drove ok. No bucking at low rpms. Still seems to be missing a little and not much power but now starts quicker. So there is progress. My question is can the o2 sensor be cleaned or is it just a replace job? I pulled the plugs and they still look clean. I'm running out of ideas. I know it can run good with the right repair but what could be the holdup?

[doobiess]

as for the o2 i dont think you can clean em.. but personally i would say replace it... since then you know for sure its ok...

[cage47]

That's the plan monday. They're only $21 so that one will be easy to get. And it's right in the front so it's easy to replace. Also going to get the new mounting plates on the cat converter so I can get that in and get it inspected again. I just hope the o2 sensor will clear up the rough idle. I'm running out of ideas or solutions. I'm slowly piecing this back together. Today I took out the remains of a cheesy car alarm. The alarm horn had been removed before I bought it and I found a kill switch under my dash. But without the remote and since it had quite a few wires already disconnected I took it all out. Mostly only had to reconnect the ignition wire.

[cage47]

So Here's the latest. Today I replaced the tbi gasket. While having it off I noticed the two bolts that join the top part of the tbi to the bottom were both loose. Tightened them. Put the new 02 sensor in. Had the new cat converter installed. Not much change. Still slight hesitation at low rpms. Nothing like it was but still noticeable from time to time. BUT then I took my tbi injector out and replaced it with the two spares I got from the junk yard. The first one was dead. The second, what a difference. It starts no problem and idles a hell of a lot smoother. Still not 100% but a lot better. And there's almost no hint of hesitation at low rpms. If it's there it's very light and not much of a problem. So tomorrow I'm just going to plunk down the $79 and get a new injector and then take it back to the shop to get the emissions redone. I also have to replace a lug nut since one sheared off. But I'm almost done. Then this weekend the strut and c/v joint and it'll be in top knotch shape, finally.

[doobiess]

strut and cv.... ok i assume your replacing both struts since you cant really just replace 1 it will give a horrible ride.. and cv shaft.. i have to say but what havent you fixed.. seems like a stuff wrong

[cage47]

I'm going to get a used strut. All I can do for now. I'm getting a new c/v and won't have enough cash left. I know they are both bad. The c/v had a torn boot and you can hear it rattling when you take right turns. I've had that happen on another car and recognize it. As far as the strut It also rattles over bumps and bottoms out the plastic under the bumper (air dam I think) on that side. But I'll be replacing both in the spring with new. But today's the moment of truth. The second emmissions test. Make or break now.

[cage47]

Well one problem licked. I replaced the intake manifold, and the egr valve and the cat converter. Brought my emissions down from 9800 to under the 1300 standard required in Tx. (the emissions shop guy said my car had the highest Nox emissions he's seen come through that shop, he didn't think it would be possible to repair, heh) so now to work out the last little hesitation glitch. Problem is I've worked through most all other items. So I'm down to some things left I was hoping it wouldnt' be. Possibly a bad ecm (going to pick a part to get another to test this weekend) or timing off, possible timing gear worn or chain. That I'll check next. But the last is a possible blown head gasket. That one I'm dreading. I can do it but it'll mean taking out the valve cover gasket and intake manifold gasket and timing cover gasket that I all replaced recently. What a bite!. I'm hoping it's just the ecm.

[rixGAphx]

Originally posted by cage47
...But the last is a possible blown head gasket. That one I'm dreading....
Have you done a compression test, including a leak-down test?

That *should* tell you if there's a compression problem.

But on an engine the age of yours, low compression results could indicate blown head gasket or burned exhaust valve(s) [especially with the high NOx values, which are a sign of WAY high temperatures].
It might indicate bad rings, but those *usually* are accompanied by blue exhaust smoke/dirty, wet plugs/dirty crankcase oil.

The only way a blown head gasket can produce high combustion temps/high NOx is if the gasket actaully leaks air IN during the intake stroke, thereby causing a very lean, hot mix.
Of course, the combustion and exhaust strokes would result in hot gases escaping thru that same gasket failure, so it would be quite noticable unless it's a cylinder-to-cylinder leak.
I don't think it's a likely condition.

I think the secret is the still-high NOx values.
These result from really lean mixture.
Your fuel pump might not be delivering adequate pressure, the fuel regulator might be reducing the pressure too much, the injectors might be dirty, the TPS might be misadjusted/faulty, or the ECM might be giving wrong signals to the injectors.

I'd say do a little more troubleshooting on these issues before assuming the worst and going 'inside'.

Good luck.
-Rick

[cage47]

That's the thing, everything you mentioned in the last paragraph has been checked or replaced. Fuel pressure all sensors, injector replaced. Now all the plugs are also new and I checked them again last weekend and they're all still fine. no buildup. And cold idle is fine but once it warms up it idles low and hesitates slightly. Not as bad as before but still noticeable. Especially when driving at low rpms. And not much power anymore. I suspect the ecm but in the diagnostic diagrams it also describes blown head gasket. I want to do a compression test but don't have the tools. But I did a vacuum check and that's fine so that leadsme to think it's not the head gasket. Another thing that I notice, not a problem since I get around it. My gas guage doesn't go all the way down to E, and the temp seems to be lower thannorm. That stuff also makes me think the ecm is screwy. But all the diags point to either the ecm or blown head gasket. And everything else is good so there's not much left to check. I lean away from teh timing gear as it idles good when cold. But believe me I've been doing quite a bit of testing to dig out this last driving problem before fixing the mechanical (strut/ cv joint). I'm so close to getting this in top-knotch condition I can taste it but this one is a bugger.

[cage47]

Heh, I did a hell of a job. My emissions went down from 8907 ppm to 6 ppm at idle and 9861 ppm at high rpm to 15 ppm. I'd say that's a big improvement.

[Colin]

Originally posted by cage47
Heh, I did a hell of a job. My emissions went down from 8907 ppm to 6 ppm at idle and 9861 ppm at high rpm to 15 ppm. I'd say that's a big improvement. Good Job , have a :beer: then do a compression check and see what turns up . ;)

[cage47]

actually, turns out my dad has a compression tool that screws into the spark plug socket so I'm going to get that and give it a try tomorrow.

[cage47]

OK. Two big problems solved and they were both my fault. First. I was going to take the aic valve back and put my original back in. Well I took the new one out and BINGO, no rubber o-ring gasket. I looked on the old one and there it was. So I put the old one back in and put the new one back in the box (save $68). And on a hunch I checked the two spark plugs that are under the alternator. Again Bingo. One was gapped at .65 instead of .6. So regapped both, and put them back in. Started the car smooth idle aside from one slight hesitation. But I drove to the store and back. No problem. Got my power back and no hesitation at speed. and no jerk and jumping at low rpms anymore. Gonna regap the other two tomorrow. So now on to the strut/cv joint. then the back shocks. I'll have this thing back to stock condition yet!

[Colin]

Originally posted by cage47
Well I took the new one out and BINGO, no rubber o-ring gasket. So the rough idle was a vacuum leak . Make sure to check your intake tract gaskets / vacuum lines / hoses to make sure there's nothing else leaking . Try gapping all the plugs to 55 ...;)

[cage47]

No. All other gaskets have been replaced. TBI unit base gasket. Intake manifold and I've closely inspected all vacuum lines. I replaced one that was worn. All others are good. The only one left is the head gasket and I'm going to test just in case this weekend (Tues Wed Thurs for me). The performance was noticably better today. What do you mean by intake tract gasket anyhow? You mean intake manifold gasket?

[cage47]

Oh, yeah, I've got the chilton's manual. But I can't find anything on the recommended vacuum pressure. Anyone have a Haynes manual that can find it for a 90 4 tech vin "U".

[Colin]

Originally posted by cage47
What do you mean by intake tract gasket anyhow? You mean intake manifold gasket? Yes , all gaskets from the intake manifold back . Don't forget along with the head gasket the compression test will turn up leaky valves and rings which can be the cause of problems .

[cage47]

Yeah, all gaskets done. I know what the compression will show me. I'm not really expecting it to show me anything unusual. I'm going to check those last two plugs and the ecm. I figure that should aleve my oscillating idle.

[cage47]

Alright. Now I'm making progress. First I found I had put my original map sensor back on last time I did some checks. Put the replacement back on and threw out the original. Runs better. But I got the compression tester and tested all cylinders. Bingo. Numbers 1, 2 and 4 all had 155 to 160. but cylinder numer 3 had only 128. So now I know where the rough idle is coming from. So when taxes come back I'm going to just go ahead and get a new head from autozone and replace all the gaskets and go ahead and replace the map sensor with a new one. Maybe replace the temp sensor also. So that's it for that for now. For teh time being I'm going to concentrate on the mechanical stuff, the back brakes, shocks and the c/v joint, and the headlight socket that's broke. Maybe the left fender also. I'll have this thing in stock condition yet.