I’m helping a buddy sort out an issue he’s having with a ‘80s L-Jet water-cooled car. This is a car he’s just about done restoring. This is the problem: The car does not idle at a constant speed. Once warmed up, the idle rises from 1000 to 1900 rpms over the course of about 1 ½ to 2 seconds and then drops back down to 1000 rpms in about ½ second. It appears to rev freely.

We have checked all the L-Jet components per his shop manual: AFM, dual relay, TPS, AAR, cold start injector, temp sensors, etc. O2 sensor replaced. We have double checked for vacuum leaks. We have also taken the AAR and cold start injector out of the loop. We’ve confirmed all the injectors are firing and that the cold start injector doesn’t leak.

Any ideas? Could it be a defective or malfunctioning dizzy? How does one go about cleaning it, assuming it's sticking inside?

Thanks.

What kind of car is it?

Have you checked for vacuum leaks?

As a search here will reveal: L-jet issues are typically related to vacuum leaks.

Start with hoses, gaskets, seals and then move on to the more difficult troubleshooting here: http://manuals.type4.org/ljet/

It's an X1/9. As I posted above, we've doubled checked for vacuum leaks and found none.

Can you explain how you checked for Vac leaks ? Having been through this, I found some ways used to check for leaks were not reliable.

First, all the vacuum lines were visually inspected. I believe one line that appeared to be inflexible was replaced. Then we used carb cleaner and sprayed it at all the various vacuum line junctions and around the large intake tube (between the AFM and plenum).

Based on personal experience with these cars, the problem is probably a simple case of demonic possession. Like mine, you may need an exorcist, not a mechanic.

Failing that, vacuum leaks. Have you checked the oil filler seal?

that car has an idle control solenoid that is prone to slow intermittent death. it was also used on the wasserboxer vanagon engines

Ask here: http://xwebforums.org/

But please, be courteous when you go there. There's some history between these two forums, so please be on your best.