Hey guys,

I'm still having an issue with a low, rough idle on my 88 when my car is cold. To recap, I go out in the morning and start the car. If I keep my foot off the gas, it'll usually drop to about 500-600 rpm and sometimes dies. After about 30 seconds it will correct itself and all is fine with my idle. I can also correct my idle by giving it a little gas a couple of times.

Even then, if I get up to 2000 rpm or so while cold and let off, it'll drop too much and almost die.

When it's warm out, it seems to start and idle fine, though sometimes in traffic it'll briefly drop into the 500's but doesn't really feel like it's going to die.

Here's what I've done:
First I cleaned my throttle body and checked my gasket. There was a little buildup on the butterflies but nothing out of the ordinary.

Then I removed and cleaned my IAC valve. I went through the reset procedure as listed in the tech tips. Just out of curiosity, I set it to be about 300 rpm too high. My idle does not reflect this. I've read that if it idles properly for a little while after resetting it, the IAC is bad. Mine doesn't reflect it even in the first place.

I've also tried holding the pedal down for 60 seconds prior to starting it when cold. This doesn't seem to change things at all.

Today I tried disconnecting my cold start injector before starting it up. I figured that it probably wouldn't help, but if I noticed no change then maybe my cold start system was bad. When I disconnected it and tried to start the car, it turned over for maybe 5 seconds before I gave up on it. I plugged the cold start injector back up and it started as it normally would under cold start conditions.

If I let it die by not giving it gas, I'll usually get a code 43. My service manual says that this is my MAF sensor, so I picked up a spare one of these and relays on the off chance that this may be it. It didn't seem to change things at all. The service manual also mentions that this code can set due to a low idle and has nothing to do with the MAF after all if this is the case.

Does anyone have any idea what I can try next? Unfortunately I don't have access to an actual scanner of any kind. Even our local "Corvette specialist" does nothing but read codes.

I don't have any big mods. I have a Power Effects cat back system and a K&N Air Filter. Otherwise I'm all stock.


[Modified by Tourney3p0, 12:23 AM 4/26/2003]

 

Find another "specialist" with the proper tools :rolleyes: A scanner is a must for troubleshooting these kinds of pesky problems. That would be my first suggestion. Second would be to hunt for vacuum leaks. I have a faulty brake booster and my car will do the same thing when cold starting. Once it warms up, no problem with the idle. I have to feather the gas a little, right after the engine catches. Good luck :cheers:

 

Does your IAC valve actually work? Will the tip move in and out? Remove the IAC and connect the wiring harness to it. Push the tip in by hand and then jump the A and B terminals on the ALDL turn the ignition to "on" and see if the tip extends. If it does the IAC is probably working.

Did you change both MAF relays with known good relays?


If you disconnect the MAF sensor does the car run any differently?

 

I think it does, but I haven't tried what you said. I'll definitely give it a try. I was thinking that since I idle well when it's warm (it'll start at 1100 or so and gradually drop down to 700 over the course of a minute or two) my IAC must be working, but I'll give that a try to make sure it's working on cold starts as well.

The relays I replaced it with were new in the box. They looked identical, but I did notice that one of the relays that was being used before I changed it was a light gray rather than black. Either way though, no change afterward.


Sure does. When I first got the code 43 I thought for sure I had pinpointed it to something in the MAF circuit. Even after replacing the relays and the MAF itself though, there was no change. Disconnecting the MAF made it run like crap, so I guess that told me the MAF was at least doing most of its job. After this is when I started doing research that told me that code 43 can give a false set due to a low idle (which I see 400-500 rpm if it's particularly cold out in the morning).

I'm going to do a more thorough test for leaks next I think.