I have a '91 Honda Civic DX hatch, PGI injection. It's not sequential fuel injected so I don't "think" it has a FITV. I could be wrong.
The following problem only occurs during the hot spring/summer season (northeast). This never happens in the winter.
Once the car is up to temperature and after driven a while the idle will stay at 2k-3k rpms when I come to a stop. Tapping the gas pedal will bring the rpms down, but it becomes severely erratic, rising and falling. I've replaced the air idle bypass valve with (2) used ones with same symptoms. New ones are stupid expensive. I don't kow if this is even the part that is causing this problem.
This just started happening to my other Civic, so this must be a typical problem with honda's.
Anyone have this problem and solved it? It's driving me crazy, especially sitting at a light with the rpms sky high.
Thanks!

 

check for vac leaks

 

check your gaskets man, i just had this problem and it turned out to be a shitty throttle body gasket