Having problems with a 1992 Z28 that keeps stalling. This has been an on going problem for a while. We thought it was a bad IAC so we cleaned that and it seemed to help for a little, but the stalling would always come back. So since Ive adjusted the idle with TunerPro, and it helped for a while but now its back. The fuel filter, plugs, wires and O2 sensor are all fairly new, and the TPS voltage seems good. The car also seems to be down in power. Its a stock 350(L98)/Auto with a few bolt on's. When and only when its warm it stalls going from park to reverse and has a couple times at stop lights. You don't need to keep your foot on the gas to keep it from stalling when shifting to reverse. You just have to barely tap the gas as soon as you shift it into reverse and the car will idle fine in reverse after that. Its just for that one brief second that the car wants to stall. So I'm thinking:

Bad Injector?
Fuel Pressure?
Vacuum Leak?
Distributor Control Module?

Any advice?

 

I tested the fuel injector resistance and found that the number one injector had a reading of 10, so I ordered a set of 22lb Bosch Design III's from FIC(The other seven all had a reading of 17). However that hasn't fixed the problem, if anything it seems to have gotten a bit worse. I'm pretty confident that its not a vacuum leak, as we labeled everything we disconnected. So today we'll probably replace the IAC Motor, and the IAT sensor in the plenum. Any help or advice would be greatly appreciated.

Thanks

 

What are your IAC counts when the engine is warm and idling in park?

 

I'm guessing thats the same thing as the steps: With the engine at its normal operating temp. the IAC steps started at 70 falling to the 60's and then to 39-40 all in about 10-15 seconds, were it stayed. When I shut the car off the steps jumped to 160.

 

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Update:

Just got done replacing the IAC Motor, and its still stalling when warm. Will probably hook up a fuel pressure gauge to it tomorrow, and have the ignition control module checked out.

 

Your IAC numbers look right to me. You have TunerPro, is your in-gear/out-of-gear value showing a change when you put it in gear? On automatics, the ECM needs to know when the car is put into gear.

 

Well with the new IAC motor the steps would eventually drop down to zero. I ran the car longer this time so that could have something to do with it. Now comes the weird part: We shut the car off, and restarted it to check the IAC steps when put in gear. With the steps at 48 and put in reverse the car didn't stall out. When shifted to reverse the steps went from 48 up to 64, then fell down to 32. From reverse I shifted to drive and the car stalled out. Restarted the car and when shifted to reverse the car again didn't stall out, but did when I shifted to drive. However when I restarted it this last time and put it in reverse the car stalled out. It seems like if the steps are below a certain number the car stalls out? Does that make sense?

 

The ignition control module passed. Removed the control module while the car was still hot, and took it down to Autozone. The guy tested it four times just to make sure and it passed every time.

While we had the distributor cap off we noticed it looked pretty bad so we picked up a new cap and rotor, and are installing it now. I Doubt this will fix it so next will be a fuel pressure test.

 

A new cap and rotor was installed. That seemed to help a little bit. If I lift my foot off the brake quick enough when shifting I can get the engine to keep running. But if I leave my foot on the brake it still stalls out. Going to buy a fuel pressure gauge later this afternoon so I can check that out. Any other ideas here?

 

Found my fuel pressure gauge so I didn't have to buy one. At a cold start I got 42 psi with the ignition on, 35 while it was running, and 37 when it was in gear. With the engine at operating temperature it was 44 psi with the ignition on, 35 while it was running, and 42 when shifting to reverse (it stalled out again). This was performed with the vacuum hose to the fpr still on.

Pulled all the plugs also today and they were pretty clean. Will test the spark plug wires tomorrow and take the coil to an auto part store to have that checked out. Running out of ideas here.

UPDATE:

Removed the ignition coil and had it tested. Was told that the primary's were in range, and the secondaries were barely in range, but still considered ok going by the books.

 

keep us posted