86 Pace car idle problem
Thread Starter
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Joined: Feb 2006
Posts: 86
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From: Gonzales La
86 Pace car idle problem
My 86 pace car idles rough, and I can't find the problem. The car starts up and runs great, and idles about 600-700 RPM's most of the time. Occassionaly while stopped with the motor idling, the car will rev up to 900 and back to 600, and sometimes it dies on me. I have replaced the IAC, and it didn't help it. Does anyone have any suggestions?
Le Mans Master
Joined: Jan 2003
Posts: 5,858
Likes: 7
From: Santa Maria CA
Since you replaced the IAC, you now need to reset the base idle speed (assuming you haven't done it).
http://forums.corvetteforum.com/show....php?t=1968281
I like to start with the basic things like checking the timing and vacuum leaks from burn or broken hoses under the hood. That can cause a fluctuating idle. I'm assuming you already did that. I also start the engine in the dark and look for any arcing at the plug wires that I can't see in the day. What's interesting is that the Engine light is not coming on even after stalling. Honestly, I'd try pulling codes anyway and see if there are any stored. Even if the light came on for a split second and went out again, there will be a code stored if the battery has not been disconnected. If there are codes, you have a starting point. All you need is a paperclip.
http://corvettebuyers.com/c4vettes/ecm.htm
http://forums.corvetteforum.com/show....php?t=1968281
I like to start with the basic things like checking the timing and vacuum leaks from burn or broken hoses under the hood. That can cause a fluctuating idle. I'm assuming you already did that. I also start the engine in the dark and look for any arcing at the plug wires that I can't see in the day. What's interesting is that the Engine light is not coming on even after stalling. Honestly, I'd try pulling codes anyway and see if there are any stored. Even if the light came on for a split second and went out again, there will be a code stored if the battery has not been disconnected. If there are codes, you have a starting point. All you need is a paperclip.
http://corvettebuyers.com/c4vettes/ecm.htm
Last edited by 86PACER; Apr 19, 2008 at 12:59 AM.
Thread Starter
Advanced
Joined: Feb 2006
Posts: 86
Likes: 0
From: Gonzales La
Erratic idle on 86 Pace Car
Well, I had the car in the shop for 3 weeks, again, and they couldn't find what's causing it. They experenced the same problem, but couldn't find the cause. They didn't even charge me for the work on it this time. The car runs great, except for the idling. Any other suggestions?
Corvette Enthusiast
Joined: Oct 2007
Posts: 6,786
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From: So. Cal.
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idleing
Does it run the same in open loop verses closed loop?
Race Director
Joined: Sep 2005
Posts: 10,878
Likes: 1
St. Jude Donor '07
My '85 had idle demons as well.
Here's what I did, one of these fixed the problem:
1. Pulled the EGR and threw it in the garbage. It may not have been seating correctly and/or the hard line was slightly cracked.
2. Doublechecked all grounds. They may have worked loose following header install.
3. Wire harness on the DS firewall. The insulation shrinked over time exposing wires that may have been shorting out across each other based on engine vibration. I taped them off.
4. Cleaned MAF and re-crimped harness wires.
5. Replaced PCV. $10 and 1 possibility eliminated.
6. Verified .47v - 4.6v on my TPS.
Now I'm idling like a monster. 700-760 without surge or stall.
Here's what I did, one of these fixed the problem:
1. Pulled the EGR and threw it in the garbage. It may not have been seating correctly and/or the hard line was slightly cracked.
2. Doublechecked all grounds. They may have worked loose following header install.
3. Wire harness on the DS firewall. The insulation shrinked over time exposing wires that may have been shorting out across each other based on engine vibration. I taped them off.
4. Cleaned MAF and re-crimped harness wires.
5. Replaced PCV. $10 and 1 possibility eliminated.
6. Verified .47v - 4.6v on my TPS.
Now I'm idling like a monster. 700-760 without surge or stall.
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