1G Idle surge

[91lzer]

Hey guys, I’ve been battling an idle surge issue for about 2 months now. It has always been an issue but the idle switch was always unplugged until I did an emissions delete and the unplugged idle switch caused it to idle at 3000 rpm. I have read that idle surge thread and have tested everything on there. New IAC, new TB seals, no vacuum leaks, set all of my sensors to factory values, etc. I have no clue what’s going on here and would appreciate some guidance. Thanks guys!

 

[Justin DuBois]

Hey guys, I’ve been battling an idle surge issue for about 2 months now. I have no clue what’s going on here and would appreciate some guidance.

1st - Boost leak test. Air getting past the TB while the closed position switch is engaged will introduce idle surge.
2nd - Coolant levels / Air pockets. When I get Idle surge, its because I didn't get all the air purged from the coolant system. The FIAV needs coolant to close down the air valve in the throttle body. If you have an air gap in the coolant lines, the valve does not get heated up correctly, so it stays open even when the engine temp reads warm.

 

[91lzer]

1st - Boost leak test. Air getting past the TB while the closed position switch is engaged will introduce idle surge.
2nd - Coolant levels / Air pockets. When I get Idle surge, its because I didn't get all the air purged from the coolant system. The FIAV needs coolant to close down the air valve in the throttle body. If you have an air gap in the coolant lines, the valve does not get heated up correctly, so it stays open even when the engine temp reads warm.

FIAV is deleted, and I just did another boost leak test and found one at the injector. It’s pretty big and didn’t notice it a month ago. But maybe that explains why the issue has gotten worse

 

[Justin DuBois]

The typical issue with a FIAV delete is a cold start starved for air. If you don't need to hold the throttle open to start, then you probably have a chronic leak.

Check your throttle body cable tension - If you can lower the idle by applying some manual pressure to close the throttle by hand - the cable is too tight.

Also check your BISS, and the ISC stepper position.