Idle Speed
Thread Starter
Burning Brakes
Joined: Jun 2003
Posts: 1,079
Likes: 1
From: Niagara Falls ON
Idle Speed
I am trying to figure out why my 86 Vette is idling really high. It seems to idle at around 1,000rpm. If I am lucky it will idle around 800. This seems high.
I have checked the timing, I have checked the IAC valve, the TPS, and checked again. It seems that when I disconnect the lead at the brake booster to set the timing it idles around 500. When I reconnected it then jumps up to 1000.
I am not getting any error codes. I used to get code 22 but I replaced the TPS but no change. Is my ECM bad? Also, my 86 is the first year with digital heating/air conditioning. Could the air conditioning be telling the ecm that it is on when it isn't acutually on?
Any help is greatly appreciated.
I have checked the timing, I have checked the IAC valve, the TPS, and checked again. It seems that when I disconnect the lead at the brake booster to set the timing it idles around 500. When I reconnected it then jumps up to 1000.
I am not getting any error codes. I used to get code 22 but I replaced the TPS but no change. Is my ECM bad? Also, my 86 is the first year with digital heating/air conditioning. Could the air conditioning be telling the ecm that it is on when it isn't acutually on?
Any help is greatly appreciated.
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
When you serviced the IAC and TPS did you reset base idle and TPS voltages? If not the method is on my site.
Incdeed a vacuum leak will cause idle problems. Check manifold vacuum at idle.
Incdeed a vacuum leak will cause idle problems. Check manifold vacuum at idle.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
My two votes are for a vacuum leak or a slipped damper ring. If the ring has moved, you may unknowingly be setting the timing far in advance of where it's supposed to be, causing a fast idle. I got the clue from your comments.
RACE ON!!!
RACE ON!!!
Thread Starter
Burning Brakes
Joined: Jun 2003
Posts: 1,079
Likes: 1
From: Niagara Falls ON
Actually I have set the timing to several settings to see how it would be affected. It doesn't matter if I set it fast or slow, the car then idles fast when the wire at the brake booster is re-connected.
I have been checking the vaccum lines but so far no luck.
It is driving me crazy because if I try to put the car into drive there is a loud "clunk". "Clunks" are not a good sign so I am trying to get the timing right and start enjoying the car for the season.
Thanks for all the advise. I will continue looking for the problem.
I have been checking the vaccum lines but so far no luck.
It is driving me crazy because if I try to put the car into drive there is a loud "clunk". "Clunks" are not a good sign so I am trying to get the timing right and start enjoying the car for the season.
Thanks for all the advise. I will continue looking for the problem.
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
If hooking up the brake booster tube is causing the idle to jump up you need to focus on the fittings on that line or on the booster itself. Use a vacuum gauge to see what's up there.
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Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by 65Z01
If hooking up the brake booster tube is causing the idle to jump up you need to focus on the fittings on that line or on the booster itself. Use a vacuum gauge to see what's up there.
1986coupe,
Have you checked for a vacuum leak at the intake manifold?
RACE ON!!!