Bad Idle--1986
Thread Starter
Heel & Toe
Joined: May 2009
Posts: 21
Likes: 1
Bad Idle--1986
Hello......Having a problem with the idle on my 1986 4 spd 350 TPI. The idle goes up and down as it pleases. Goes from 800 rpm's up to 1500, 1600 to 1700 rpm's at times.....then at a red light it will go back down to the 800 rpm's. I've changed the plugs, wires, distributor cap and had the injectors checked out. Mechanic said the timing is ok too. I was told there might be a computer chip problem.....and it wouldn't be a hard fix. Or.....am I looking in the wrong direction ?????? Thank you for any help I can get. Grant
gnf1953@***.net
gnf1953@***.net
Pro
Joined: Feb 2009
Posts: 655
Likes: 164
From: Vancouver Washington
idle
Here is a link for a site that explains exactly how to set the base idle on your car.
http://www.docstoc.com/docs/25331704...-thru-1992-Not
The instructions are the same as what is in the factory service manual. Worth the investment if you are going to do any of your own work on the car.
http://www.docstoc.com/docs/25331704...-thru-1992-Not
The instructions are the same as what is in the factory service manual. Worth the investment if you are going to do any of your own work on the car.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Wandering idle like this is a prime symptom of a vacuum leak. The ECM goes crazy trying to compensate for the extra air. It sees that the mixture is too lean so it adds fuel. The RPMs go up. It backs off the fuel so the RPMs drop.
An incorrect minimum idle adjustment can also cause a problem like this. Do this first and see what happens. If not fixed, look for a vacuum problem.
jazfe posted that while I was typing, so I didn't see it until I posted my response. I don't agree with changing the TPS voltage, as recommended in that article.
An incorrect minimum idle adjustment can also cause a problem like this. Do this first and see what happens. If not fixed, look for a vacuum problem.
jazfe posted that while I was typing, so I didn't see it until I posted my response. I don't agree with changing the TPS voltage, as recommended in that article.
Last edited by Cliff Harris; Dec 5, 2011 at 01:56 AM. Reason: Added note about jazfe's post.
Instructor
Joined: Sep 2007
Posts: 233
Likes: 0
If you find after checking the vacuum you still have the same problem of surging idle. I would definitely take a look at you ECM. My 1986 had a severe problem of erratic idle and surging. After chasing down a few vacuum leaks which did not fix the problem. My mechanic changed my ECM and the problems went away.
As an aside I have been once again dealing with a weird idle problem outlined in another post. This time it seem to be possibly sensor related. I mention this just to say the ECM is very sensitive to all the components around it.
As an aside I have been once again dealing with a weird idle problem outlined in another post. This time it seem to be possibly sensor related. I mention this just to say the ECM is very sensitive to all the components around it.
Team Owner
Joined: Jul 2004
Posts: 28,430
Likes: 3,279
From: Hartford WI
I would remove the TB, the IAC and the IAC housing. Clean them all with Brake Cleaner and then reassemble. After which, I would check things out with my scantool. I look for 15-20 IAC counts and adjust to get that. This is assuming there are no leaks. To check for leaks, use a propane torch WITHOUT the flame being lit.
