I have a 83 trans am with the 305 crossfire TBI. I am having issues with the idle when starting the vehicle. Sometimes it idles fin but lately every time I run it it seems to idle in park at like 2300-2500 rpm. Could this be the IAC's or what. The car sat for eight years and I just got it running. When you put it in reverse or drive it drops down to normal at like 1200 rpm. I recently replaced the front throttle body with a old one and it ran high. changed the IAC and it ran fine again. Now it's idling high again and I'm stumped. Anyone have any ideas?

 

most likely vacume leak or sluggish IAC is the cause,
also check for binding linkage. does it run rough when
idling high? Also check the plug for the CTS-they are
known to corrode and deteiorate,often replaced with
'85 up style plug and CTS when bad.