Idle Problem
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Joined: Oct 2007
Posts: 84
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From: Denver NC
Idle Problem
~~Continuing my story about my 1992 vette purchase on Ebay.~~
My vette has some obvious mods including Corsa exhaust, throttle body and MSD ignition.
It has been idleing rough when I slow down at red lights or in traffic. It bounces between .5 and 2k. Occassionly it boggs out and cuts off so I have to shift to neutral when stopped to keep the RPMs up.
There is a Chevy dealership in walking distance to my house so I took it over there for their opinion. They refuse to work on it because I have an aftermarket computer or PCM. (there computer would not work to pull codes).
I was unaware of the aftermarket computer. I have heard everal things saying that the computer might need to be reflashed. I heard it could also be the o2 sensors. The fuel pump and fuel filter is brand new. To mee it seems to be running too rich. The car runs great when it's in motion (like highway or open street).
There is a guy who programs PCMs up the street from me about 20 minutes. I think I might take it to him. He does PCM programming for everyone - you might know him (www.pcmforless.com)
Any suggestions of what else it might be. I just had the brakes redone and if I can get the ide fixed I could actually enjoy this car I just bought.
thanks
My vette has some obvious mods including Corsa exhaust, throttle body and MSD ignition.
It has been idleing rough when I slow down at red lights or in traffic. It bounces between .5 and 2k. Occassionly it boggs out and cuts off so I have to shift to neutral when stopped to keep the RPMs up.
There is a Chevy dealership in walking distance to my house so I took it over there for their opinion. They refuse to work on it because I have an aftermarket computer or PCM. (there computer would not work to pull codes).
I was unaware of the aftermarket computer. I have heard everal things saying that the computer might need to be reflashed. I heard it could also be the o2 sensors. The fuel pump and fuel filter is brand new. To mee it seems to be running too rich. The car runs great when it's in motion (like highway or open street).
There is a guy who programs PCMs up the street from me about 20 minutes. I think I might take it to him. He does PCM programming for everyone - you might know him (www.pcmforless.com)
Any suggestions of what else it might be. I just had the brakes redone and if I can get the ide fixed I could actually enjoy this car I just bought.
thanks
Race Director
Joined: Jan 2004
Posts: 18,726
Likes: 710
From: Bergen County, NJ
There is a Chevy dealership in walking distance to my house so I took it over there for their opinion. They refuse to work on it because I have an aftermarket computer or PCM. (there computer would not work to pull codes).
As far as your idling problem; 1st check the IAC. Idle air control valve.
Others can chime in, like I said, I'm no expert.
Race Director
Joined: Apr 2004
Posts: 17,066
Likes: 3
From: Milpitas ca
You can pull codes on the ALDL by yourself with a paper clip.
Maybe replacing or cleaning your PCV valve might help. Its only a 2 dollar part. IAC would be my next check.
I don't think there is an aftermarket ECM
Maybe replacing or cleaning your PCV valve might help. Its only a 2 dollar part. IAC would be my next check.
I don't think there is an aftermarket ECM
Advanced
Joined: Sep 2007
Posts: 95
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From: South Jersey NJ
Check for vacuum leaks. Something like a PCV hose or Booster line leaking will drive the ECM crazy, causing the IAC to fluctuate up and down trying to obtain the desired idle. Also if your engine has a MAF sensor, you might have a leak between it and the throttle body, or an air leak at the throttle body gasket. A bad MAF sensor can sometimes be diagnosed by lightly tapping it with the wooden handle of a hammer, with the engine idling, and see if the engine changes in the way it idles.
A TPS will cause this symptom, but will usually trigger a check engine light. Anything else you will probably need a scanner to diagnose. Just because the dealership says it won't communicate, doesn't mean its true. Maybe try to find a reputable private shop that knows what they are doing. Whatever you do, don't start guessing and replacing parts, as it can get expensive. I doubt you have a problem with your computer, but it does happen from time to time.
Good luck!
A TPS will cause this symptom, but will usually trigger a check engine light. Anything else you will probably need a scanner to diagnose. Just because the dealership says it won't communicate, doesn't mean its true. Maybe try to find a reputable private shop that knows what they are doing. Whatever you do, don't start guessing and replacing parts, as it can get expensive. I doubt you have a problem with your computer, but it does happen from time to time.
Good luck!
Thread Starter
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Joined: Oct 2007
Posts: 84
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From: Denver NC
Part of my problem is that I cant find someone to take a look at it. Dealership wont touch it. Speed shops around here said they mainly do Fords.
Anyone in the Charlotte, NC area? (Huntersville, Moorseville, Indian Trail)
I dont have the equipment (or the knowledge at the moment) to do this myself.
Anybody have any quick tips on how-to?
Anyone in the Charlotte, NC area? (Huntersville, Moorseville, Indian Trail)
I dont have the equipment (or the knowledge at the moment) to do this myself.
Anybody have any quick tips on how-to?
Racer
Joined: Aug 2006
Posts: 403
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From: Huntsville Alabama
That's the problem I had on my '96 LT1. I found my PCV hose was burnt on the bottom side. Wouldn't know it unless you removed and checked. Very simple to do...
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Thread Starter
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Joined: Oct 2007
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From: Denver NC
Advanced
Joined: Sep 2007
Posts: 95
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From: South Jersey NJ
Look for a white, rectangular label under your hood. There should be one with a diagram of all of your vacuum lines. Listen for any hissing noises. Another sign of a possible vacuum leak would be the PCV chattering, after you find it of course. See if your throttle plate has a set screw to adjust the throttle angle, could be too low, making the IAC over compensate. Maybe try cracking it open a bit more, a little bit at a time, if you don't find a vacuum leak first. Also, you might have some throttle body coking. If you take the boot off of the throttle body, look inside the bore, and see if there is any carbon build up around the throttle plates. You can clean it with some carb cleaner on a rag.
Hope this helps. Alot of drivability problems are usually simple mechanical problems rather than sensor failures. Usually, but not always, will a sensor failure trigger a check engine light, and throw a code.
Hope this helps. Alot of drivability problems are usually simple mechanical problems rather than sensor failures. Usually, but not always, will a sensor failure trigger a check engine light, and throw a code.
Advanced
Joined: Sep 2007
Posts: 95
Likes: 2
From: South Jersey NJ
Also, make sure that the CHECK ENGINE light even works. When you first turn the key on it will turn it on for a few seconds for a bulb check. If the previous owner was having trouble before he sold you the car, he may have taken it out.
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Joined: Oct 2007
Posts: 84
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From: Denver NC
It turns out that my vette had a few performace mods that I was not made aware of. The computer had problems with the stock settings running the mods. I took it to a shop to have it dynoed. After a 1/2 hour or so I gained 51 hp and it now runs like a brand new car. Mechanically the car was fine it just needed to be tuned. I was told to put a stock throttle body back on becuase they work better than the aftermarket one it had. I was also told to gut the cat which would help it breathe even better.
Heel & Toe
Joined: Mar 2006
Posts: 21
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From: Lago Vista TX
On my 92 when I changed to an Accel ignition my tach was acting wierd and would drop to 0 RPM if you floored it. Did a search on this website and found that there is a tach filter on the 92. So I cut it out and it solved my tach weirdness and therefore the computer was getting correct RPM data and then ran much better. You might look for this post and see if you still have the factory tach filter. That might be some of you problem(s).
Melting Slicks
Joined: Nov 2002
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From: 1993 Quasar Blue 'vert Scottsdale AZ
Melting Slicks
Joined: Jan 2005
Posts: 2,604
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From: Phoenix, Arizona
Originally Posted by Accupulse;1562665818There is a guy who programs PCMs up the street from me about 20 minutes. I think I might take it to him. He does PCM programming for everyone - you might know him ([url
www.pcmforless.com[/url])
