birdblack

After some recent modifications to my Ls1 I’m having an issue with the motor idling fast. The recent modifications were a Fast 92, a Fast 92 throttle body, and Holley valve covers with Ls9 coils. The Formula had an oil catch can before the modifications. My problem is after the recent modifications at times the motor wants to idle and run at 1800/2000 RPM. Driving the car, it’s like the car is on cruise control. When I come to a stop the motor will fast idle for 6 - 8 seconds before falling back to 900 RPM. And it doesn’t happen all the time which is odd to me. When it’s not fast idling, turning on the air conditioning will bump the RPM’s from the normal 900 RPM to 1800/2000 RPM. Any ideas? Maybe I should also mention the motor previously had a head and cam swap.

Floorman279

iTrader: (11)

try the relearn on the tps sensor. i forget what it is exactly but search for it. if you have a scanner, see what your tps is open at at idle.

i ended up having to lengthen the throttle cable on mine. with the car off, try to gently push the blade closed with your finger. if it closes with a little effort, lengthen the cable by locating the little black box in the middle of your throttle cable, and lifting the lock latch and extending.

Chevy406

iTrader: (12)

Verify you do not have a vacuum leak. If the engine idled fine before the intake & throttle body then you most likely have a vacuum leak.
Verify your throttle blade is closing onto the stop (like Floorman mentioned)
Try adjusting the throttle blade stop screw counter clockwise to allow the throttle blade to close more (really need to be monitoring IAC while you do this)
Beyond these checks you will need to start adjusting your idle Base Running Airflow table

birdblack