I have a 1994 Vette Base and I have checked all over for vacuum leaks and can't find any. I replaced the Idle Control Valve and nothing has changed. I don't think it will be the Mass Air Flow since it's in the hose from the air filter to the throttle body. I'm at a loss!!!! Any ideas on what else it can be?

 

Molesen Welcome back. I see this is not going to be an easy issue, there are a few things you can check. You checked the EGR and you said it checked good, could be internal vacuum leaks? but I wonder about the EGR gaskets under the EGR valve, (maybe) leaking or bad gasket. Throttle body may need to R&R to clean and inspect for leeks (cracks-bad gaskets) Also another thought may be a bad intake gasket, between the intake manifold and the cylinder head. (almost impossible to hear). You can check the intake manifold bolts to see how tight they are first,tighten if needed and see if that makes a difference idling, they may need replacement. You can do a test where you take a board or something rigid and block off the intake tube from the air cleaner when running. It should kill the engine almost immediately. You said it ran smoothly at higher RPM making me think air getting in somewhere, ruling opti-spark or fuel injector. Hope this helps.

 

Yes I'm back after 1893 miles! I will give your suggestions a shot. I think the first thing I try is blocking off the air intake hose from the air cleaner. That sounds like a good idea. I didn't think the EGR would cause it but I've been wrong before! Thanks for your continued help on this matter and have a good day!!!

 

Another thing to look at is your timing. It could be too far advanced or stuck in an advanced position. I don't have a 94, but thinking it has a conventional distributor. The mechanical advance in the distributor may be an issue.

 

I'm also not getting any codes

 

You won't always get codes if a sensor is out of adjustment, only if it's shorted or readings are completely off the mark, normally. The timing is advanced through the ECM I believe. Might check and see if the distributor is tight. There are issues of the water pump leaking water on the distributor causing problems. I still think it's a vacuum leak or maybe the tps sensor could be off. Best way to tell is with a digital multimeter and check the readings at idle position to see where they are. O2 sensor maybe out of spec. Sorry for all the guessing. Hope it helps.

 

I'll check and thanks for all the help.

 

I changed the mass air flow last night and that didn't work either. When it's plugged in it idles at 2200 RPM and if I unplug it it drops to 1500 RPM. I'm going to recheck for a vacuum leak again.

 

I rechecked for a vacuum leak and I don't have one. I've changed the mass air flow and the idle control valve. Nothing has changed. I did notice that on the throttle body the plug for the adjusmant screw is gone but I can't see what kind of screw is in that location. Anyone have an idea? I looked in the throttle body but the flaps look ok and I can't see if they are closing properly. I don't know of anything else to change except the throttle body? Any more ideas?

 

It almost sounds as if the ecm is not reaching closed loop. I think they make a code reader these days for checking that or you can do it the old fashion way with a dwell meter, and the green wire on the distributor. I think you reached the point where you need to know what the ecm is doing..