K_Gunn2128

I bought a 1991 Camaro 3.1 v6 TPI two years ago out of a barn. As to be expected after staying in that barn for so long, rats had chewed wires under the hood and a few parts had gone bad... after working on the car for nearly a year, it was ready to drive.. or so we thought.

After I started driving the car on a regular basis, I noticed that it had an idling issue, especially during the hottest part of summer. As long as you're going down the road the car runs fine, but if you have to stop at a stoplight the RPMs start bouncing up and down, anywhere from 500-750 RPM. Unless you hold it on about 1500RPM, it will eventually flutter and die.

This issue has just about driven us crazy. It seems almost like it's flooding; the cooler the air is, the better it runs. We've tried changing the temperature coolant sensor and it seemed to do better for a while, but now (er, when I parked it for the winter) it's back to square one. I've never had it scanned, therefore no codes to guide us.

Sorry for such a long post. Any advice would be greatly appreciated... A friend mentioned that it could be the computer? Never messed with fuel injection much, so it's safe to say that we're a little lost.

RBob

iTrader: (1)

Do an idle learn first and see how much better it is.

If the injectors are the stock ones then consider replacing them.

RBob.

Base91

iTrader: (1)

You've got to start with good injectors or nothing else matters. If it's all original you almost certainly need new injectors and probably a new diaphragm in the fuel pressure regulator. Did you clean the idle air control valve housing? etc.etc. etc.

K_Gunn2128

RBob I take the battery cable off of it every night after I put it in the garage. Didn't know until earlier today that you're supposed to do an idle learn every time you put the cable back on. Could very well be part of the problem.

I personally have never changed the injectors, and if I was guessing I'd say they're the original ones. And no, I hadn't thought to clean the idle air control

ItstillaV6

How do you do an "idle learn"? I only ask, because, every time I disconnect my battery, I have to pull the IAC valve, reset it per the Haynes manual instructions, and then drive the car. Otherwise, it'll stall out if I let off the gas, while driving, and start decelerating for a long period of time.(i.e. coasting down a freeway exit ramp)

Basically, I can be cruising, let off the gas, watch the RPMs hold at around 1200 or so, then when I get down to about 20-25mph, the car sputters and stalls.

Granted, my IAC valve was pulled from a '97 Monte Carlo 3.1L, so I have considered that to be part of the problem. Yet, when I reset the shaft and reinstall, I can drive it and after a few miles it seems to be fine. The idle will hold around 1100rpm, when decelerating and around 750-800rpm with the engine at normal operating temp.(my stalling issues aren't just IAC related, the car has a huge misfire under 1500-1700rpm and I get code 43 occasionally)

RBob

iTrader: (1)

Here is the original thread:

https://www.thirdgen.org/forums/v6/1...ght=idle+learn

There is another that I can't find at the moment. In it I describe how to clean the TB and the TB blade. This too helps with low speed and idling. With the EGR being piped in right behind the throttle blade that area gets quite filthy.

It is important to clean the edges of the throttle blades. And the bore of the TB where the blades are when the throttle is closed.

RBob.

HiPerf_Chevyman

Any luck with this?

K_Gunn2128

None yet; haven't had time to try it. Hopefully will get to this weekend. Are you having a similar issue?

ItstillaV6

Thanks for the info. I read the procedure, and it is a little different then what the Haynes manual describes. However, it sounds very familiar to what we did, when my Quad 4 had to be replaced, in my 93 Grand Am.(Shocker there!)

We actually had the battery disconnected, for over 2 weeks(that boat anchor had to drop out the bottom, because it was 5-speed), and when i went to start it, the mechanic that was helping me said the car had to re-learn the idle. We had to let it idle up for a longtime, in gear, before he would let me shut if down.

That was also a $3500 lesson learned, on why you avoid Quad 4's, like they have a disease.

K_Gunn2128

Update on this... took the car and had injectors replaced, had several other things checked (EGR Valve, etc.) And the mechanic promised that he had test driven the car and that the issue was fixed. $350 later, I drove the car home and before I could make it there, the car had already died on me. Same issue, low idle like it's flooding. I have attempted to do the idle learn and for whatever reason (this car is stubborn; go figure) the fan would not cycle through that day. Where do I go from here?

HiPerf_Chevyman

well to start, id make a plate to block the EGR, just to be sure the ECM isnt opening it part way....

The IAC is surely working fine? when this rough idle happends... what happends when you crack the throttle open?

The ICM check out okay???? Sometimes when they get weak, Heat is their worst enemy..

these cars are so simple compared to todays. and being OBD1 its hard to test things with a scan tool. like the EGR. if it isnt closing 100% after being opened, you will get a rough idle..... and OBD1 doesn't allow us to check this, hence the idea of a solid gasket.. my car had on it. i didnt even know it was there until i thought i'd see how clogged the ports were lol. Maybe its the same issue. i left the plate there. somebody put it there for a reason, and i dont want to find out why going to work some morning in a Thunderstorm

K_Gunn2128

Dad mentioned making a plate to block the EGR, I believe we are going to try that in a few minutes.

IAC seems to be working fine. When you crack the throttle open it runs perfect. The only time it runs bad is when you're sitting at say a stop light, etc. Unless you hold the idle at about 1000-1500 RPM it dies... trust me lol

What is the ICM?

mcrandrz

Ignition control module. Located under the distributor cap and rotor. Behind the intake plenum. Its a part I carry a spare with me at all times.

They seem to fail only when its hot. Very annoying. But a 10 min repair. Because you can just move the distributor out of the way instead of removing all the wires and redoing all that.


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Stewie

Takes 15-20 minutes to replace. Just to add on to mcrandrz's advice. There is a small packet of grease with the ICM. Use your finger to smear some of the grease on the metal plate on the bottom of the ICM before installing. The grease insulates the ICM, otherwise the heat will cause the ICM to fail prematurely.

Cadaver_Puncher

Always keep a spare ICM in the little rear glove box thingy. Screw getting stuck in BFE when it goes bad.

K_Gunn2128

Blocked EGR Valve off a few minutes ago... still no luck. The idle seems to be smoother overall with the EGR blocked but every so often the RPM will dip down almost to zero, and the car will sometimes catch itself and go back to idling fine or go ahead and die. Before it will start back I have noticed that I have to turn the key off and back on. When I took the car to have the injectors replaced I know that the mechanic did have the distributor cap off and cleaned everything, but in his notes it doesn't mention the ICM. What do your cars do when the ICM goes bad?

And thank you all for the advice, it is very much appreciated!

W.E.G.

armos

Have you tried cleaning out the IAC passages? I saw it mentioned but not if you did it.
When the idle starts bouncing, what happens if you electrically unplug the IAC? This will prevent it from moving. Does that stabilize the idle, or does it keep bouncing?
This could be interpreted as that the IAC is having trouble passing enough air. Cool air is more dense. But most likely, it could be anything that's having a heat sensitive problem, it wouldn't have to be the air temperature that's the issue.

For the flooding theory:
You could try unplugging the O2 sensor. This will leave the car in open loop, so it will command rich even when warmed up. If you can smell that it's richer this way, and it's idling better, then it's probably not a flooding issue.
Note: this doesn't mean it's lean - a rich mixture sometimes just masks other problems. It's not good for the catalyst though.

This is odd. I can't think of anything here except fuel pressure. Turning on the key primes the fuel pressure for a couple seconds. However, the pump should also run when cranking. It's as if that's intermittently failing.
Hook up a gauge to measure the fuel pressure, and watch how it acts as the car warms up and begins to run rough. Check if it has pressure when you try to restart.

K_Gunn2128

armos, I haven't tried anything with the IAC yet. I did buy a new IAC but was wondering if there is a specific procedure that I need to go through in order to install the new one correctly. As far as O2 sensor goes, that was one of the first things I replaced hoping to fix the problem. We also tried unplugging the MAP sensor a few days ago, again with no luck.

mmadden55

Do you have a tac? And is it bouncing?

K_Gunn2128

The car has the original tach in the dash but yes the RPM is bouncing up and down. The amp gauge is also going up and down but not sure if that is a related issue or something else entirely

fasteddi

iTrader: (2)

If the tach is bouncing arround a whole lot I believe it's related to the tach output on the ignition control module Flacky IAC

scury13

Any luck on solving the problem? Having pretty much the same issue and have tried a ton of things with no luck. I can give more info on what I have done if anyone wants it.

K_Gunn2128

Scury, haven't been on here in a while, but no I still haven't had any success on solving the issue. Not sure what to try next.

huber16

I'm sorry that you are still having trouble. I've been reading this thread since my car is having the same symptoms. Of course, the right answer is best but knowing the things which did not work is helpful to. I was wondering if you got your car fixed. Thanks for writing back with a progress report. Good Luck!

Maverick H1L

iTrader: (8)

From experience, if the tach is bouncing, the ignition module doesn't have long to live. I'm talking a couple weeks at most.

Replace the ignition module and the fuel injectors. Get a fuel pressure gauge and test the fuel pressure, which should be between 37 and 47 PSI.

Get a multimeter and check the resistance of the intake air temp sensor and the coolant temp sensor with the engine COLD. They should be nearly the same reading.

You will also want to check the voltage between the black and gray wires at the MAP sensor (to check baseline voltage, which should be at or pretty close to 5V), and the green wire and the black wire with the engine running.

willexoIX

Plus 1 on the ICM. My tach is bouncing and i get spark dropout, should have mine replaced in a couple days.

If the fuel injectors are original, id replace them anyway. Your call on the injectors, but definately replace your icm, and dont forget to clean the surfaces where it mounts and use the thermal paste. You can use what comes with it, but im using Arctic Silver Ceramic 5 thermal paste on mine.

huber16

I will check the temp sensors and MAP voltage. My tach has not worked in years. Is there a test which can be done on the ignition module (it's original to the car)? I also got a vacuum gauge and thought that it might help identify a vacuum leak. I don't know how much vacuum the 3.1 is "supposed" to pull though.

Update: I checked the MAT and ECT with my ohm meter and they seem pretty close. One measured 8.8 and the other 8.9 on the 200K scale. The shop was about 35 deg. F when I checked them. I also hooked up the vacuum gauge and its only pulling 14-16 in Hg. This seems a bit low so I looked more for vacuum leaks. I sprayed ether where I thought that it might be sucking air but the engine never sped up. Spraying highly flammable liquid on a hot engine does make me a bit nervous. There is a T fitting on the back of the plenum. One side goes to the brake booster and the other side goes down the rear of the engine. What does the line going behind the engine do?

scury13

Well, I cant say for sure if my issue is resolved as its not been hot out since my last repair. I have replaced the ICM along with countless other parts over the summer. The last thing I did in the fall was a complete rebuild of the dizy. Prior to that I had swapped the ICM twice but made no difference. Replacing every thing else in the dizy really seemed to help. Not to mention the o ring was shot causing an oil leak I had thought was a rear main but turned out to be the dizy o ring. Since I did this the car has not stalled or reved erratically when slowing down or at idle. There was still a hint of the idle dropping a tad and coming back up but nothing, I mean nothing like before. However, i wont be confident until summer returns and see it is still working. I also resolved my gas tank pressure issue by replacing that pressure release valve that connects before the charcoal canister, not the one at the gas tank. Oh and I hunted down the air dam and baffles and put them on which helped the car run cooler while driving down the road. Maybe a combo of all these but rebuilding the dizy seemed to be the real difference maker for now.

K_Gunn2128

I still haven't managed to figure out what's causing the issue with mine. I had wondered about ICM but haven't changed it yet. It hadn't been as bad this summer but lately it's back to its old ways again. Next step will most likely be ICM... or a carbureted 350 engine swap. Whichever comes first

Will keep you posted on what I come up with. Thanks to everyone for your input.

K_Gunn2128

Also had a guy tell me once that the charcoal canister could have something to do with it. How would I go about checking that to see if it has an affect on the idle?

80TAwannabe

I'm. having the same problem with my firebird

,tried all the above and replaced everything, injectors,fuelpump distributor including cap wires and plugs, fuel pressure reg.still idles eratticly but runs great

92RS-HeritageEd

iTrader: (2)

Same Issue, 92RS 3.1L V6 (LHO), RPMs fall below 1K damn thing dies . Can anyone provide a detailed list of areas to check? Also, while cleaning the IAC Valve w/ BPC or Carb cleaner can you physically spray the cleaner into the opening to clean out the "carbon deposits" or whatever the hell the black residue is lol causing the IAC to become "sitcky"?