Matro

I just got my 1990 Camaro RS with a 3.1 MPFI v6 and 700r4 about a month ago. I have had a few problems with idling and cold starting.

First off, whenever I start the car after it has sat overnight or longer than 24 hrs, it takes a little longer for it to turn over and the engine will rev really high and then low, then high, then low, etc... This will happen for about 15 seconds then slowly settle down to a steady idle speed.

Secondly, once the car idles for a bit, it will slowly begin to idle at lower rpm's and begin idiling very rough. The same happens if I sit at an intersection. Sometimes it idles fine, and other times it is really rough. I put it into neutral and the idle will slowly climb back up but once I go into drive, it jumps back down and the car keeps trying to lurching forward. The even stranger part is that the engine will stall and the SES light pops on. It will even die sometimes. But once I start driving again the SES light turns off and there is no problem until I stop again.

Now I have looked at different reasons for this but i can't figure out how to fix it. I found it REALLY strange when I took off my entire air intake, intake temp sensor, and idle air control valve and cleaned them with some WD40. I put everything back together and surprisingly, I started it up and there was no high rev and it idled perfectly (I mean perfectly!) for about 15 mins and then it went back to crap.

Someone please help me I have no idea what is causing my problem...

Thanks,
Matro

defaced

iTrader: (6)

I would recommend throwing a new IACV and TPS at it. I don't think they're very expensive and that kind of sounds like that's what the problem is.

Matro

Why would my TPS be faulty if my acceleration is fine? There is no problem accelerating or staying at high speeds. It only screws up when I'm at a complete stop.

defaced

iTrader: (6)

Never really considered that. I would look more at your IACV then.

CamaroDon

I'd spend some time looking around for a vacuum leak as well; my '89 2.8 behaved exactly as you described, and after replacing all of the sensors with no real improvement, I finally nailed the problem to a bad gasket on the EGR tube where it attaches to the intake plenum. I discovered it after spraying carb cleaner along all of the vacuum lines while the engine was running. I replaced the gasket and it ran like a champ. Good luck...

MyIrocz,noturs

do you think it would be possible for you to post pictures of that gasket u were talking about because idk where the egr valve is.

CamaroDon

I'm not sure how it looks on your 3.1 but here's a pic from my 2.8. The EGR tube is the metal corrugated pipe running up and out from behind the alternator in the lower left corner of the photo. The bad gasket I encountered was where the EGR tube attaches to the air intake, concealed from view underneath the brass-colored IAC valve in the right-hand center of the picture. If your idle problem is indeed due to a vacuum leak, it could be any vacuum line and not necessarily this particular gasket, but it's a good a place as any to start. With the motor running, I started spraying carburetor cleaner along all of the vacuum lines and connections, and the change in idle quickly pinpointed my leak for me.

Matro

Thanks for all of the feedback guys! I will go look at my vacuum lines and I already ordered an IAC so I will see if that fixes the problem.

91specialk

my experience with TPS is, there is usually only a problem at idle, but I think it is more likely a problem with your EGR valve or a vacuum leak associated with the EGR. Just my 2 cents. I know i need a new EGR valve. Took it off to inspect it and it rattles, but after 20 years what can one expect?

Matro

the IAC came today and I replaced it. When i first started it up, my car sounded horrible.....barely being able to stay alive. When I shut it off and came back to it in a few minutes, it ended up sounding a lot better. I will know if my problem is fixed for sure after I drive it tomorrow.

Matro

Turns out i had the EXACT same problem... the IAC didn't change much at all but i checked for leaks and that same gasket is causing my problem. I plan to get a new gasket ASAP. Thanks for all of the help everyone!!!

Matro

well.....i guess this case isn't closed yet after all.......

i got the new gasket....and my idle got a little better. The SES light doesn't turn on anymore.

Still....when I spray carb cleaner over the rubber sealwith the 2 plastic hoses coming from it on my throttle body, the idle revs up like it did with my EGR gasket.

would that be another vacuum leak that i have to worry about?

because my car will start to raise in RMP's all by itself if it idles for a little while and when i tap the accelerator, it will jump up and go back to the low RPM's.

all advice would be very helpful to help diagnose what is going on.

CamaroDon

Yep, it does sound like there's still a vacuum leak or two going on...which could definitely explain the lingering idle issues. Something to be aware of is the fact that carb cleaner spray tends to disperse readily, and a change in the idle from the spray may be indicative of a vacuum leak in the vicinity of where you're aiming, but not necessarily right where you're pointing the spray. I found this out when I was spraying around the TPS; the vapor was actually finding its way to the vacuum leak at my EGR tube gasket, just beyond and underneath the TPS. But at least you have a good idea as to where to concentrate your efforts.

johnman330

Mine used to do that, Mass Airflow Sensor fixed it, theres a relay for that too. I also had to play around with the vacuum hoses on the back side of my manifold just above the distributor. Honestly im 90% of the way done replacing all of my sensors, switches, and relays. Already did the timing chain, fuel pump, fuel pressure regulator, oil pressure switch and harness, water pump, starter, alternator, the interior is next then the body. Good luck on yours.