LT1 Erratic Idle

[FlyingDutchman]

Originally Posted by ThoR294

usually its the one-way valve in the pumps. vapor lock is virtually impossible in fuel injection systems due to the pressure the fuel is under.

What if you prime it 4 times when its warm, does it start normal?

Well yeah, if the system maintained pressure like it should, but it's not lol so I went and bought a pump, stay tuned.

[townsend]

Originally Posted by 97camaro

Been chasing this issue for more than a year now, hopefully someone has some insight ! I will try to provide as much info as possible, mods in sig below.

While driving / car moving, my rpms in neutral will sometimes climb or stick to (after pulling out of a gear) 2000 rpms with no throttle input. Putting it back in car the car will maintain speed around 2k rpm in 1st to 4th (instead of DFCO). When I come to a COMPLETE stop, the rpms will drop back to normal idle (750rpm). I also had an issue where the idle would hunt on cold start, but it hasn't don't that in a while. It was acting this way last night, but I didn't have anything to scan/ log with..

Potentially related issues include: long starts after car is left alone for more than 10 minutes, feathering the throttle seems to help a lot; surging/bucking at low rpms, and sometimes requires fair amount of throttle to start in first or it dies / bucks like crazy with not enough throttle (makes starting from a stop unpredictable).

I think I've ruled out vacuum leaks since it's intermittent, happens hot or cold, and spraying carb cleaner around didn't make a difference.

Parts I've replaced since my engine rebuild:
CTS
ICM
Coil
Plugs
Wires
Fuel pressure regulator

I also pulled the IAC out and sprayed it with MAF cleaner and WD40, didn't look any cleaner.. this part is currently at the top of my list cause it could affect all of the above. However, the logs I have seem to suggest the IAC is working.

Any ideas??

i had this problem with my 96, and chased all the same parts youve changed etc to no avail. mine would randomly rev as well up to 2k rpm at idle with no throttle input. turned out my opti was screwed up, heat soak was causing opti signal to spike a random rpm signal to computer, which in turn would open iac up. replaced it and never had a problem since