KeithO

I just had the radiator and all cooling hoses replaced on my 88 IROC 5.7. It is now behaving strangely. I am not sure if this is related to the current problem.

Prior to having this work done, the engine idled rock steady at about 650rpm and sounded beautiful (with the Dynomax cat backs). Now, the idle jumps around and it has a noise. Symptoms:

1) The idle jumps around when at a stop (whether in neutral or drive). Just about when it is going to stall (About 350-400 rpm), the lights go dim and it picks up the revs and 'hunts' for calm. Sometimes it settles, sometimes it doesn't. During the rpm oscillations, the light go dim on the lower revs (probably more of an effect than a cause).

2) When standing in front of the car at idle, it has a noise (I also notice this noise when driving by 'Jersey Barriers' - the sound reflects). Not quite a squeak, not quite a hiss. This noise is constant. When I open the hood, I can't track the noise down.

3) If I brake to a stop under hard or moderate braking, the car stands a good chance of stalling - and has on a few occasions.

I'm an old carb guy and kinda lazy sometimes. If it were carbed, I would probably bump up the idle and forget about it. However, I want to do this right.

Has anyone seen this?

ede

seems funny it happened at the same time as the other work, but i can't think of any related parts they could of messed with. i'd look at the IAC, see if it's dirty or needs replaced. check fuel supply, volumn and preasure.

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ICON Motorsports
1st & 3rd

gsmann

you know, i had the same problem and nobody could figure it out. i changed the 02 sensor, temp sensor, set IAC, cleaned it everything. then some guy connect a battery jumper cable to the negative post to anywhere on the chassis and see if it fixes the problem. and it did. so i connected a ground wire from the battery to the chassis. i don't understand what it was but it fixed it. check it out, it might help.

ViciousZ

iTrader: (1)

Yes, I've seen this problem. In fact, I see it every day because my car is doing the same thing! I can't for the life of me figure out what the problem is, and unfortunately neither can my mechanic. But seeing as how I've been trying to solve this problem for the past few months, I've got quite a few suggestions. First of all, the dimming lights is a result of your low engine speed causing low alternator output. The most likely thing that causes this bad idle is the IAC motor or other IAC related problem. First, make sure there isn't any carbon built up in the IAC passage. Then check to make sure you don't have a short in one of the wires going to the IAC. You can do this by unplugging the IAC connector while the car is running and grounding a test light to each of the four pins, one by one. The light ought to flash for all of them. I'm not sure how to check the IAC motor itself, but maybe someone else around here knows. Other things to check: TPS, fuel pressure, vacuum leaks, defective PCV, bad ECM, bad ground, MAF, O2 sensor, misadjusted minimum idle, timing, fuel filter, and the general condition of the ignition system. Some more obscure causes that have been suggested to me are a defective park-neutral safety switch (I have no idea why) and bad power steering pump or switch. If you are having major drivability problems, you might try this as a quick-fix: Wait till the car is cold. Start it up. When the idle is steady and around 750 (you can turn on the AC to raise the idle if you need to), pop the hood and, with the car running, unplug the connector going to the IAC. This trick may or may not work for you, but it worked for me. The only problem with this trick is that it will give you major cold-start problems. To put it in carberator terms for you, it'll be like starting a car without a choke. You gotta keep your foot on the gas for the first few minutes. But if it keeps the car from dying at every single traffic light, it may be worth it.

airbrushguy

Sounds vacuum related to me, check the lines epecially the MAP lines and that sensor. even the base gaskets, sounds like you have problem related to brakes because tthere isn't enough inches of vacuum availabe for power brakes.

KeithO

Just to update you all that have this "problem".

I drove the car to work this morning and the car's idle was again rock steady. Also, I did not hear the noise described above. I think it is safe to assume that the behavior and noise are related.

I suppose the difference between when the happens and when it doesn't is the type of driving.

On Sat. when I had the problem I was doing alot of stop-n-go driving. In addition, I was shutting the car off frequently (I was Christmas shopping).

On my drive to work, it's pretty much smooth sailing with a few stop signs to contend with.

FYI