My 1989 Firebird Formula 350 suddenly won't idle. My wife parked it and came out 3 hours later and she had to keep her foot on the gas in order to start it and keep it running. I looked around the engine & didn't see or hear any vacuum leaks, loose wires, loose hoses, etc.

When you give it enough gas to just idle it sounds a little rough & smells rich. Once above idle it runs fine, AC on or off.
The car has 160,000 miles on it & runs strong. It has the dual converter exhaust & WS6 package if that matters. Thanks.

 

If it is a Tuned port injection, the idle air control valve may have gone bad. It has a square electrical plug that plugs into it and sits right under the throttle position sensor on the throttle body.

 

How do you test it?

 

There is a tool for that. However I don't know where you can get one. You can also grab the throttle cable and check to see if the throttle blades stick at any point as you move them into the WOT position. If they stick, you at least need to clean your TB.

 

Is there no way to test it with an Ohm meter?

 

Oil level? May be a little too low..

 

You can test the continuity of the operating coils of the IAC steppere motor with an ohmmeter, but you can't monitor IAC activity. I'd suggest removing ht eIAC, cleaning the throttle body and IAC air passages completely, cleaning and lubricating the IAC, and checking the TPS voltage at idle. You may end up resetting the throttle minimum air position as well.

 

Success! 1/3 of a can of carb cleaner later.

Al I did was blast away at the throttle body & IAC passage. Actually filled the passage & let her sit for a few.

Thanks for everyones help.