Possible low idle problem
Thread Starter
CF Community Team
Joined: Nov 2005
Posts: 5,248
Likes: 2,888
From: Charlotte N.C.
Possible low idle problem
I might have a problem starting.....
A few weeks ago I drove to West Virginia, 600 miles, to visit my son. It was wet most of the trip, rain or fog or both. After the visit it was nice and sunny and when I started the car, 92 coupe 6 speed, it wouldn't idle well, running about 4-500 rpm. As long as I kept the car going it ran well, it was just an idle problem. After the car warmed up it got better, the high idle while rolling functioned as it should. The next morning it did the same thing. The morning after that it was fine, started idled at 900 or so and idled at 1200 while the car was rolling. Hasn't had the problem again until this morning. A cold but sunny day and the car would barely run 4-500rpm until it warmed up and then it was fine. I would say that the idle up function is not working but it's idling lower than 900. No codes or lights, all gages look good.
Any ideas? vacuum leak? Injector starting to go?
Oh, I forgot, this was just after putting Seafoam in through the intake and 3/4 of a can in the full fuel tank.
No throttle body on an LT-1...
A few weeks ago I drove to West Virginia, 600 miles, to visit my son. It was wet most of the trip, rain or fog or both. After the visit it was nice and sunny and when I started the car, 92 coupe 6 speed, it wouldn't idle well, running about 4-500 rpm. As long as I kept the car going it ran well, it was just an idle problem. After the car warmed up it got better, the high idle while rolling functioned as it should. The next morning it did the same thing. The morning after that it was fine, started idled at 900 or so and idled at 1200 while the car was rolling. Hasn't had the problem again until this morning. A cold but sunny day and the car would barely run 4-500rpm until it warmed up and then it was fine. I would say that the idle up function is not working but it's idling lower than 900. No codes or lights, all gages look good.
Any ideas? vacuum leak? Injector starting to go?
Oh, I forgot, this was just after putting Seafoam in through the intake and 3/4 of a can in the full fuel tank.
No throttle body on an LT-1...
Last edited by EvanD; Jan 10, 2007 at 08:09 PM.
Pro
Joined: Nov 2006
Posts: 638
Likes: 0
From: Plano TX
Maybe spend a few bucks on a bottle of throttle body cleaner, toothbrush, and a gasket. I had some idling issues, pulled mine out and did a thorough cleaning of the IAC and TB. I went ahead and performed the steps to reset my idle and my TPS (I had my TB completly apart) and now it runs like a charm.
Melting Slicks
Joined: Oct 2004
Posts: 2,510
Likes: 4
From: Austin Texas
all FI LT1's have a throttle body! The FI delivers the fuel, the TB delivers the air!! Unless someone dropped a non-FI carburated engine in your '92. The above suggestion of cleaning you TB sounds like sound advice. You could have carbon buildup on the TB shaft which makes it stick at colder temps. I would also take a wild stab at a bad O2 sensor, but that would throw an error code. Next, I would run my tank to about 1/8 full, then load up on premium gas, see if that clears up your erratic idle.
Last edited by MikeC4; Jan 10, 2007 at 11:18 PM.
Thread Starter
CF Community Team
Joined: Nov 2005
Posts: 5,248
Likes: 2,888
From: Charlotte N.C.
OK I know there's a throttle body, I was lost for a moment thinking about my Camaro that had a throttle body that was like a carburator...
OK clean that and the IAC. The IAC makes a lot of sense as when I did the Seafoam it could have washed junk down stream...
Now all I have to do is figure out where it is....
Thanks!
OK clean that and the IAC. The IAC makes a lot of sense as when I did the Seafoam it could have washed junk down stream...
Now all I have to do is figure out where it is....
Thanks!
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
The IAC is on the bottom side of the throttle body. I would recommend either using the old gasket if in good shape or making one from gasket paper. Use "throttle body" cleaner on both and a toothbrush or small brush.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Idle speed is a function of engine temp. Scan it to see what the ECM is receiving from the Coolant Temp Sensor. On a cold engine, the temp reading should be about the same as the outside air temp. Otherwise, spend 9 Bucks on a new sensor. Check it's resistance cold and then check the resistance of the installed sensor. Both should be close. If not, simply plug the new sensor into the harness and start it. If the idle is correct, replace the sensor. If the resistance of both sensors are close and if the idle speed is still whacked out with the new sensor plugged in, that might indicate a faulty ECM. A clue would be if the fan is running with the engine cold and the a/c off. A scan would provide greater certainity.
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Team Owner
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From: Fort Knox, KY
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Check your PCV valve also. They tend to get neglected at tune-up time. Cheap fix and preventive maintenance, too.
Thread Starter
CF Community Team
Joined: Nov 2005
Posts: 5,248
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From: Charlotte N.C.
Today it starts and idles perfect..... I'll go get some cleaner.....
Last edited by EvanD; Jan 11, 2007 at 01:15 PM.
Melting Slicks
Joined: Oct 2004
Posts: 2,510
Likes: 4
From: Austin Texas
here's a good, understandable writeup of the PCV's function:
http://www.misterfixit.com/intakman.htm
http://www.misterfixit.com/intakman.htm