1986 high idle
Thread Starter
Cruising
Joined: Dec 2012
Posts: 14
Likes: 0
1986 high idle
The car had a very high and surging idle.replaced the injectors, replaced some old brittle vac lines, and this made the car run and idle much better but instead of the 1200 rpm idle it still idles at 900. replaced plugs and wires, fuel pressure is in check, replaced iac valve and set idle to 550 per Haynes manual. After setting the idle it "stuck" and I thought it was fixed. But after the initial idle set, once it is restarted after a drive it goes right back to 900. The tps has been repeatedly set to .54 after every idle reset. Any ideas?
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
A high idle is almost always a vacuum leak. Try removing and plugging all the vacuum connections to the plenum. That includes the brake booster, the two fittings on the rear passenger side and the one under the throttle body. I had a vacuum leak at the hose where the PCV valve tube attaches to the intake manifold.
Another possibility is an EGR valve that's stuck open.
It's also possible that the ECM is seeing low coolant temperature and you're in "fast idle" mode. Check the CTS (Coolant Temperature Sensor) on the front of the intake manifold under the throttle body. They're pretty cheap, so it might be easiest to just replace it.
A scan tool will tell you what the ECM is seeing and might help you determine what the problem is.
Another possibility is an EGR valve that's stuck open.
It's also possible that the ECM is seeing low coolant temperature and you're in "fast idle" mode. Check the CTS (Coolant Temperature Sensor) on the front of the intake manifold under the throttle body. They're pretty cheap, so it might be easiest to just replace it.
A scan tool will tell you what the ECM is seeing and might help you determine what the problem is.
Le Mans Master
Joined: Feb 2005
Posts: 6,481
Likes: 566
From: Clearwater Florida
........ The Haynes manuals are helpful ... sometimes ... but a Factory Service Manual from Helms is worth its weight in gold ... you can find them on the parts for sale forum from time to time ... get one ... you'll be glad you did ..............
