Weird idle issue.
 

I have a nice 800rpm idle when the car first starts up. After some driving, the car will sometimes just idle up to ~2000rpm at stop lights. It's not surge, it's a steady idle. Any ideas on why it's doing this? It's a 1992 gsx 5spd btw.

Re: Weird idle issue.
 

mine was doin this too. i ended up replacing the isc and adjusted the bov. and it went away. i dunno, it helped for a while but now i need a head gasket, and it does it after it gets hot. Don't know if this helped at all but good luck

Re: Weird idle issue.
 

is your throttle body sticking open?

Re: Weird idle issue.
 

My guess would be ISC, FIAV, or maybe a vacuum/boost leak that only acts up when everything is up to temp.