The question I see a lot! Why does my idle bounce?
- In a 90/91 they have a FITV (fast idle thermal valve). Tightening this can resolve this issue. (check your manual)
- For non-FITV vehicles this is a vacuum leak / or leaky seal past the throttle body. Intake gasket or IACV gasket, etc.
- It can also simply be a bad IACV. This is 90% of the cases as the car is old and the IACV is old. See your manual for testing the electrical leading to the IACV and also the ohm reading on the IACV. Even if these test fail you take off your IACV and inspect it for dirt. Clean and bench test if possible.
Before - Dirty! Nasty! IACV can barely move.
After cleaning...
IACV testing with 12V signal. (quick 1 second connect should move the actuator)
View attachment 20250704_201847.mp4
- In a 90/91 they have a FITV (fast idle thermal valve). Tightening this can resolve this issue. (check your manual)
- For non-FITV vehicles this is a vacuum leak / or leaky seal past the throttle body. Intake gasket or IACV gasket, etc.
- It can also simply be a bad IACV. This is 90% of the cases as the car is old and the IACV is old. See your manual for testing the electrical leading to the IACV and also the ohm reading on the IACV. Even if these test fail you take off your IACV and inspect it for dirt. Clean and bench test if possible.
Before - Dirty! Nasty! IACV can barely move.
After cleaning...
IACV testing with 12V signal. (quick 1 second connect should move the actuator)
View attachment 20250704_201847.mp4