Bad Idle When Running Warm
Thread Starter
Racer
Joined: Nov 2000
Posts: 351
Likes: 0
From: Allen TX
Bad Idle When Running Warm
Whenever my '94 gets above 210 or so, the idle will have split-second jumps over 1000 RPMs. Normally the temp is around 195-200 so there is no problem, but when I run the A/C in stop-and-go traffic, the temp will get as high as 225 and that's where the trouble is. Sitting at a light, the RPM's will jump, very quickly (half-second?), and sometimes, if I'm not really pressing on the brakes, the car will roll a couple feet (freaks me out 
). It will do this every 10 seconds or so but it's not constant, like you can time it. With the temp up around 210, even if I turn the A/C off, the RPM's will jump. Any ideas what's causing this? The Opti has not gotten wet and the car has about 56,000 miles.
). It will do this every 10 seconds or so but it's not constant, like you can time it. With the temp up around 210, even if I turn the A/C off, the RPM's will jump. Any ideas what's causing this? The Opti has not gotten wet and the car has about 56,000 miles.
Instructor
Joined: Feb 2000
Posts: 176
Likes: 0
From: Villa Ridge, Missouri
Still could be the Opti..
My first one lasted about 60k miles, the second one lasted 75k miles.. Both with similar problem you are having. They all will wear out eventually.
Have you been able to pull any error codes?
My first one lasted about 60k miles, the second one lasted 75k miles.. Both with similar problem you are having. They all will wear out eventually.
Have you been able to pull any error codes?
Thread Starter
Racer
Joined: Nov 2000
Posts: 351
Likes: 0
From: Allen TX
I think I'll try to find the tips I printed out on how to pull the codes. Didn't sound too hard but I've never done it before. Don't you think if it was the Opti though, that it would do the "idle jumping" all the time and not just when it's warm/hot? 
Thread Starter
Racer
Joined: Nov 2000
Posts: 351
Likes: 0
From: Allen TX
IAC, that's under the throttle body right? Sounds like a weekend project. If I remember correctly, someone in another thread said that some plastic piece could be real brittle around the IAC, does that sound familiar. Last thing I want to do is turn this into a major problem.
Melting Slicks
Joined: Jun 2004
Posts: 3,032
Likes: 4
Originally Posted by 94Controller
IAC, that's under the throttle body right? Sounds like a weekend project. If I remember correctly, someone in another thread said that some plastic piece could be real brittle around the IAC, does that sound familiar. Last thing I want to do is turn this into a major problem.
I can't speak for your LT1/4... on my L98 this is what I did: The IAC is on the bottom of the TB. I loosened the throttle body, to where i could get a wrench on the IAC and took it out. Took about a half hour to do that. The pintel on the IAC gets carboned up pretty badly and that causes problems with idle, and causes a slight movement when your sitting in D at a stoplight or somewhere. I'm not sure what plastic piece your talking about. If your IAC is the same as mine, it will be a pretty solid unit... I believe that there is a tech tip for removal of the IAC on your car.... give it a look
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Sounds like the IAC isn't keeping up with the load of the compressor or that it isn't increasing/decreasing rpms as the a/c clutch cycles (which is why it surges). If cleaning/replacing it doesn't cure it, you'll need to have it scanned to make sure the PCM is responding to the a/c signal. You might also want to have the a/c system checked out. Above 70 degrees, it shouldn't be cycling at idle (if it's fully charged) and your engine temps sound a bit high with the a/c on. Could be the compressor is headed south so make sure you can turn the outside hub with little resistance (engine off) and that there isn't a gob of a/c oil on the hood above the compressor.
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Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Forgot to mention that the compressor clutch may be slipping too. Look for rust colored dust around the front of it. With a feeler gage, make sure that the air gap between the outer hub and the pulley (engine off) is no greater than .020 in.
Instructor
Joined: Feb 2000
Posts: 176
Likes: 0
From: Villa Ridge, Missouri
Originally Posted by 94Controller
Don't you think if it was the Opti though, that it would do the "idle jumping" all the time and not just when it's warm/hot?
But like some of the others have said here, could also be the IAC, coil, ignition module, vacuum leak.. etc..
If it were me, I'd start with the easy stuff (clean the TB and IAC) and work up to the harder = $$$ stuff till the problem was found..
Good luck..
Racer
Joined: Oct 2003
Posts: 475
Likes: 21
From: CLAREMONT Ca
Idle
Mine is doing the same thing. As a matter of fact, I too have a '94 Polo Green Vette. The first place I will begin is to check the IAC and see if it needs cleaning. I am hoping its not the Opti. That would blow.
