Idle on a 2008 pontiac torrent drops and then goes back up to normal
Happens usually when in drive and foot on brake,usually when waiting at a long stop light idle will drop and then in a second or two then jump back to normal then drop and then back up to normal and so on.
Cars & Trucks - Pontiac
Answers & Comments
Do a fuel system clean on it if that doesn’t work then you’ll need to replace the iac idle air control unit or throtlebody also take brake cleaner and spray around the intake to check for any intake leaks if the car idles up when you do that you’ll have an intake leak
This might be from the radiator fan cycling off and on, or it might be from the air conditioner cycling off and on. Some engines have a solenoid that gives the engine more gas when things like the A/C unit engage because they place a much larger load on the engine. If this solenoid is not working, then the engine won't be able to automatically compensate for the heavy load of the A/C unit.