I've owned my car for almost a year and a half now and it's never idled right. It's always been high, around 1,500 RPM. It never really bothered me, I always assumed I had a vacuum leak somewhere (probably LIM) and that I would fix it when I had another problem that would make me work in that area. Now the weirdness begins yesterday, I was stuck in traffic and suddenly she's idling perfectly at ~800... So this got me to thinking that maybe my fast idle cam is out of wack and since I was stuck in traffic the temps rose high enough to make the wax rod disengage and set the idle straight. To make things even weirder today my idle started to bounce from 1400 to 1600 RPM's with no load on the E/L, if I turned the lights on it would settle down to 1500, but with no load it bounced up and down. It did this for about 2 minutes and then stopped. So now I'm confused, is it a problem with the E/L unit, the fast idle cam, or something else? Jumping 10 and GND has no effect on idle either so I never screwed around with the 2 adjusting screws on the front of the TB. How can I check the fast idle cam? It's so hard to see when the TB is on the car.

 

Let me ask you this, have you ever changed or adjusted your throttle position sensor (TPS)??? Or the high idle might be leaky intake gaskets check with carberator cleaner around the upper manifold and then again at the lower side where it attaches to the motor. Your looking for it to raise the idle where ever you spray it. Start with the easy stuff first before checking for a leaky intake gasket make sure no vacuum lines have come off. Good luck take your time you will find it.

 

I've never touched the TPS, I have checked for leaks with carb cleaner on all the intake tract components EXCEPT the LIM. The idea of spraying carb cleaner in the vicinity of the turbos scares me a bit. Just to be safe though I have changed all the gaskets, UIM-LIM, UIM-TB, TB-Elbow, and I've done a silicone hose job, all hoses replaced and tie wrapped or glued in place with weather stripping adhesive. The ACV has been replaced and both it's gaskets were changed too. The LIM to engine gasket should have been replaced when the turbo's were replaced just before I bought the car, but I don't know for sure if it was since I didn't do the work myself.

 

I've got almost the same problem with my car, and I've checked pretty much everything and I'm pretty sure its the LIM gasket. I've done the vacuum hose job, replaced all the same gaskets as you, checked the TPS, IAC solenoid, and all vac hoses, and can't find any problems.

To answer your fast idle cam question, you should be able to tell if its fully disengaged by checking if the throttle stop hits the adjustment screw/locknut on the front of the throttle body. When my engine is cold, the fast idle cam keeps the throttle plate open slightly, and you should be able to see this.

On a side note, in my quest to try and figure out my high idle problem, the other day I removed the rubber hose that connects the intercooler to the plastic elbow that bolts to the throttle body. With the engine running, I completely covered the opening of the elbow with my hand (I felts lots of vacuum). My idle dropped *maybe* by 50 or 100 RPM. It seems to me that I have a leak so bad that my engine is getting enough air to idle at 1500 to 2000 without getting ANY air through the throttle body. Any thoughts one this? I doubt a simple vacuum hose leak would cause such a big problem. I'm just dreading pulling out my turbos just to replace the LIM gasket.

Paul

 

Check your clutch switch too.
Its the switch that in front of the clutch. When you press the clutch it suppose to stick out about 1/2 inch. Mine stick only 1/4 inch, and my idle is hunting under load. I just replaced mine today, and it works. No more idle hunting. Although my idle under no load still bounce +- 25rpm.
The switch is cheap about $20.

Try check your clutch switch first, cheap solution if it is broken...

Reza
'93 Silver FD

 

If the fast idle screw gets too loose, it will back out on it's own. Try moving the fast idle cam back and fourth to see if your idle changes. I had the same senario where the idle was always high, and at times would fluctuate. It did turn out to be my fast idle cam. I did need to readjust my Air Adjustment Screw to get everything perfect.

 

Thanks to everyone who replied. From what you've all wrote I'm thinking that my fast idle cam is most suspect (and easiest to test) so I'm going to try moving it while the car is warmed up and running to see if it effects the idle. I'll post the results once I've done it.

reza - Thanks for your reply, but my car is an automatic so no clutch switch for me But I'm going to be at Sevenspeed in 11 days for my 5 speed swap I can't wait!

 

Sorry for digging up an old post... but i need some help here

I have the same symptoms described here where my idle stays high at about 1300rpm. Without any electrical load (lights off, ac off, defroster off, etc.), the idle would bounce from 1000rpm to 1300rpm whem I'm rolling and coming to a stop and the idle bounce would vanish as soon as the car comes to a complete stop. However, with the parking lights on or the headlights on, this does not happen at all and the idle would stay steady at 1300rpm regardless of whether or not the car is coming to a stop.

Anyone have ideas what could fix this problem?

Also, when I step on the brake (with the headlights on), the dash would dim for a quick second (actually less than a second)... is this related to the problem mentioned above?

Thanks

 

Have you reset your ECU recently? If you do, it needs time to learn your idle.

 

I've reset my ECU a few time lately. how much driving time does it usually take for the ECU to relearn the idle?

 

You have to let it sit at idle for 10 min., then let it idle with defrost on for 10 min, then let it sit with AC on for 10 min. Even after that, sometimes my car still acts weird...it usually clears up in a short amount of time though.

 

i thought thats the idle learning procedure for the PowerFC ECU..... the stock ECU has to go through that idle learning procedure too?

 

Can someone confirm this?

I had my car idling alot to make sure i dont have any leaks from the coolant hose i replaced. Today was my first time out in a week.

But even have some driving, and some hesitation, the car idles like 1300rpm. Hesitation goes away after like 3 minutes of actual driving but the high idle is still there.

I remember my car used to act like this and only ran better the more times i used it but i dont remember the high idle.

 

Mine never did.