High Idle AFTER 20 mins of driving....could it be fuel issues?

[Red97GST]

After warming up, my car idles at the normal 800rpm.

After my car heats up, and i drive it around for maybe 10-20 mins, the idle will stay at around 1200-1500rpm. It wont waver up and down, it will just choose an RPM and stay there.

The car has been doing this for months. I recently had a blown head gasket replaced, and figured maybe the problem was stemming from the overheating I was experiencing.

But the problem remains there. EGTs will be higher, at around 500 C, rather than the usual 400-450C. I attribute this to the higher RPM, though, more than any real overheating.


I'm running essentially a stock set up. T28@15psi with a stock fuel system minus the 190lph walbro.

The car will idle fine after it warms up. But after some city driving, the idle will go up, and STAY up.


I haven't tried messing with my BISS screw or anything else, as I assumed if I lowered the idle when the car is heated up, that it will idle too low until it is driven harder, and this only masks the real problem anyway.


I believe the o-rings on my 450's are going bad. Not sure if this could have anything to do with it. I know the car is running real rich after putting in the fuel pump, as indicated by the blackness above my muffler on the rear bumper.


I couldn't find similar issues when searching for idle problems. Any input??? Thanks in advance

 

[blackGSX2g]

I would suspect a either a vacuum leak after your throttle body, or a too tight throttle cable. Its possible that it gets tight enough to slowly increase the throttle once its warmed up.

 

[Red97GST]

hmm i didnt think of the throttle cable being too tight. could it just tighten on its own over time? i havent messed with it in years.... but i will check that out tonight

 

[blcknspo0ln]

I've seen a couple different things happen..

bad (or improperly adjusted) TPS
bad ISC
stuck throttle cable
the "stopper" on the TB has something stuck on it
BISS out of adjustment..