How to: Solve a 1st Gen Idle Problem

Solving an idle problem in a 1st Gen can be very vexing. The 1st Gens have layer upon layer of vacuum and electronic systems to regulate the idle. A trouble shooting list for idle problems covers every major component on an engine.

I've outlined a few of the more common fixes to try to help you out.

Surging idle or too high idle: Causes and fixes.

There is an air bubble in the coolant.
Bleed the coolant while it is hot and running. The bleed screw (12mm) is located next to where the upper radiator hose connects to the head through the air screw in front by the top radiator hose, where it goes to the engine. Also, make sure the radiator cap is on tight and both caps on the overflow tank are tight, and that there is enough coolant in the tank.

There is a vacuum leak
One by one, disconnect each and every vacuum hose on the engine. With it disconnected, plug the hose and the fitting it connected to. If nothing changes, move on. If the problem goes away, closely examine the hose and any other hoses that connect to it. Look for cracks, holes, or tears that could allow air in. Don't forget the brake booster line! A new hose will fix the problem.

The Throttle isn't shutting completely.
Detach your intake tube and look into the throttle body. Both brass butterflies should be snug against the round walls of the throttle body bore. If they are not, check and see it there is too much tension on the throttle cable, and make sure it is relieving all tension when the throttle is off.

The Fast Idle Controller isn't closing.
On the back of your intake manifold, there is a vertical cylinder with a couple of coolant lines going into the bottom. The top is a cap held on by two screws. If you have AC, there is a vac line off it to a small canister next to the brake cylinder. This assembly is the Fast Idle Controller. Its purpose is to let extra air into the manifold while the engine is cold, when the engine warms up the air passage gets closed off and it should idle normally. What was happening on mine was that the plunger that closes off that air passage wasn't closing all the way. This let it idle too high, or caused the idle to surge.

To check and see if this is YOUR problem too:
Remove the screws and take off the cap (I recommend getting an impact driver for ALL philips head screws on an engine that haven't been moved since they were installed in Japan in the 80's. They are really jammed tight, and it is easy to strip the threads. One tap with the impact driver will pop them loose). Under the cap you will see a black disk with a hole in the center. After you car is warm and it is surging, use your finger to plug this hole. If the surge goes away and it idles normally - BINGO!

To fix this problem:
Either buy a new Fast Idle Controller for $55, or fix it with a $.29 O ring.
I used the O ring and it has worked fine so far. You need to unscrew that black disk somehow, but the slot is wider than most screwdrivers. I used a small nailpuller, but a scraper would work as well. There is a spring underneath that disk providing tension. When it is off, you will see the plunger underneath that is supposed to plug the hole in the disk. Place a 3/8" rubber O ring on top of that plunger, then screw the disk back on. Be very careful, its easy to crossthread this disk as it is only plastic. You will tighten it down all the way.

Start it up and let it warm up again. The O ring should allow the plunger to seal the airspace again, curing the idle surge problem.

Your Idle is set too high
HA! Trick Problem! You can't set your idle too high, because the system is supposed to regulate the idle automatically! Well, that's Hondas line. However, it is doubtful that after all these years you can turn that idle screw without destroying it anyway. Don't bother even thinking about the idle screw, the problem lies elsewhere.