Fast Idle

[terry mckeown]

I just finished replacing my injectors (Accel), gaskets (Jerry's), wires (Hamilton Chevy). First time for me, it went great, thanks to DYNOMITE for your help, much appreciated.
One minor problem, when the engine is hot, I have a fast idle 1100 rpm, a few times at a red light it did drop to 900, but most of the time it stays at 1100. Does anyone have any advice on how to cure this problem.

[A26B]

Terry,
Doesn't idle fast when it's cold?

Sounds like a vacuum leak.

[Z51JEFF]

You got a vacuum leak.

[1990 quasar blue]

Did it start after the swap or has it always done it? If it did it before, there is updated code for the PROM to address that. A quick check for a vacuum leak is to turn on the key with the engine off. After the vacuum pump stops, time how long it stays off. Mine will go several minutes. Good luck.

[tccrab]

Vacuum leak would be the most likely cause of your high idle.
Try loosening the plenum bolts and then re-torquing them in the correct order.
What condition are your PCV tubes?
The F tube on top and the connecting hose on the bottom are notorious leakers.
The MAP sensor hose gets gummy and leaks too.
This is the funky connector just behind and under the plenum.

A handy dandy shade tree mechanic tried and true vacuum leak checker you can use is good ole propane.
Use one of those hand held propane torch cans, the one the plumber uses to solder copper pipes under your sinks.
Start the engine and let it come to operating temperature.
Crack the valve on the propane can until you can hear the propane hiss slightly. What you want is a light hiss, not a loud hiss.
DO NOT light the gas, rather, hold it an inch or so away from all readily accessible vacuum connections and around the base of the plenum.
If necessary you can attached a rubber hose to the torch so that you can direct the flow with a lot more precision and flexibility.
When your idle speeds up your leak is found.
Remember, propane is extremely flammable and you must be careful when doing this.

Good luck!!

TomC
'Crabs

[terry mckeown]

Thanks for the info Tom, I just finished going over the entire engine with the propane bottle and hose, couldn,t find the leak. However I did check the plenum bolts. I originally torqued them to 20 lb. ft., when I checked them today they were around 12 to 15 lb. ft. with the engine hot. I re-torqued to 20. Still no change in the idle 1100-1200 rpm. Your right that double connector under the pcv valve is sloppy, do all the connections have to tight ie. have hose clamps on them. The double & single connections seem to go on and off pretty easy. What is this prom fix people talk about.

[terry mckeown]

Tom one thing I forgot to mention when I turn the key on the vacuum pump runs for about 5 sec. then it,s off and on every 6 seconds for a short time say 2 sec. run time.

[Demps]

Check the vacuum hose under the throttle body. Use a flashlight from drivers front. The hose spirals and ends in a side-by-side rubber gromet in the plenum valley.
Ted

[bldavis11]

Originally Posted by terry mckeown

Tom one thing I forgot to mention when I turn the key on the vacuum pump runs for about 5 sec. then it,s off and on every 6 seconds for a short time say 2 sec. run time.

This pretty much seals that you have a vacuum leak. I agree with Tom's advice from above. It's down there somewhere, and might even require you the take the plenum off again to find it.

[A26B]

Terry,
As others have said, it's probably one of the connections under the plenum. If/when you pull the plenum, also check the fit of the injector in lower, primary o-rings. if the fit is not snug, vacuum can leak at this location also. That o-ring is in a groove, inside the injector housing.

Hope you find your problem easily.