I just picked up an 87 GTA with the 350 in it a few days ago, and was told by the old owner the check engine code has randomly been coming on for a month or so with an O2 sensor error code but he didn't notice any impact from it. I drove the car for a bit with no issues, and the same on and off check engine light and yesterday the problems started. I went to start the car and it just would not crank. I waited a few hours and had the same problem. I then noticed that as long as I am giving it gas it will work, and the instant I let off the gas it stalls. If I ride this way for a few blocks it eventually runs fine although idles a bit roughly. The check engine light flickers on and off, and I noticed that the oil pressure is much higher than it should be when hitting the gas, and then drops to almost nothing when I let off the gas. I have driven the car for short trips around the neighborhood 2 additional times with identical results. Before I start tearing things apart, does anyone know what would cause this? Would it have something to do with the O2 sensor? Thanks

In general I notice my vehicles run better if I keep up on the maintenance. And I get better gas mileage and a bit more "spunk" when replacing a very old oxygen sensor with a new one. I read these should be replaced as a regular maintenance item every 60,000 miles.

I don't think this would cause your problem though.

When you say it will not crank, does this mean you turn the key to start and the electric starter motor does not turn?

Or do you mean the electric starter works and sounds like normal, but the engine will not start? (Unless you press on the gas a little...)

This sounds like a problem with the IAC valve. Also the throttle position sensor "turns on" the IAC valve when the throttle is completely closed. If the throttle can't close completely because it is dirty, then it will not activate the IAC valve.

The IAC valve is an electric motor which adjusts to allow more or less air into the engine at idle. This is computer controlled. Remove the valve. Do not turn on or start your engine with this valve removed! (The plunger will go flying off into the hedges if you do.)

Then look inside the hole and be sure it is clean. And make sure the air passages at the end of the hole are clean as well.

Use throttle body cleaner to clean everything, DO NOT get cleaning solution on any of the electrical portions or these parts.

Also your engine gets air from the PCV valve at idle. Clean that valve and associated tubes and be sure air can flow through the tubes.

After IAC reinstalled, you can test it with a paper cup and a string. After running, then shutting off the engine, the IAC "pintle" will move all the way forward, then half way back. You can hear this movement with the paper cup "phone" and string tied to the IAC valve or its electrical connector...