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]

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.

[terry mckeown]

Thanks Jerry for the info. I will probably pull the plenum again next week and check to fit of the new injectors, I did oil the O rings in the primarys and put oil on all the O rings on the injectors, however inserting them in the holes in the injector housing was tight and maybe I was too rough. Is it possible that one of the O rings moved or came out of the groove?
I have sniffed all the vacuum lines and connections and around the joint where the plenum meets the injector housing with propane twice and still no luck. I do know that the 2 lines under the plenum are connected could see them with a flashlite. Another question I have if if the PCV is faulty how would that effect the idle.
Thanks again to all for the help.

[scottfab]

uh, before you yank out the plenum or engine make two quick checks.
Does the idle come down if you punch the throttle hard a few times?
If so..

1. take off the bellows and then get the high idle condition to happen. Next reach in with you fingers and push on the throttle plates to see if they'll close more. If they do the idle may come down. I use a small amount of axle greese on the edges of the plates.

2. check the IAC (mounted on the RF of plenum) for contamination (carbon).
Do NOT clean it completely as it has a special grease on it.

[terry mckeown]

Well I finally found my vacuum leak. I used a smoke machine connected to the plenum and found the vacuum line that connects to the plenum left front on the underside. I was able to reach it by removing the throttle cables and the throttle mechanism. Took me about an 11/2 hrs. but I was able to get the hose on about 1/2 inch. Started the car and bingo, she idles at 650-700 rpm. Thanks again to all who helped me, you guys are great.

[gbmidyear66]

Hmmm - I have the same sympton as you Terry, but I don't believe mine is a vac leak - my vac pump does not cycle - and I had same symptom before replacing my injectors.

I am going to start with the IAC, then the throttle plates.