HIGH IDLE...Whats wrong with my engine?

[turbospyder19]

sometimes ill be driving along and push the clutch in and then the cars idle will drop so fast the car will die and i have to restart the car. then other times i will be at a stop light just sitting there idleing and the idle will go up from 700-900rpm to like 1500-2500rpm my foot is off the gas and we have already checked for a vacuum leak and there is not one. does anybody know what else could be wrong? the car is also completely warmed up.

any ideas will be greatly appretiated.

 

[1glaserturbo]

How is your ISC (Idle speed controller) It's located underneath the throttle body and you can check it via www.vfaq.com

Also, go ahead and turn your car off, screw in your BISS (base idle set screw) completely in, then 180* outward. Let us know if that helps!




Chris

 

[90 TSI FWD]

my laser does that too every now and then.. when the car is off and i put the key on the "ON" position, i hear noises from the ISC motor, so im pretty sure thats the problem

 

[blcknspo0ln]

I don't know how many times I have to type this out, so i'll make it short

Check your ISC via the 2 step procedure from VFAQ
Make sure your FIAV is not clogged/not working
Check your TPS to see if it properly adjusted
If you have done the 1g TB mod, make sure you are using a 2g TPS
Adjust your BISS with the ISC disconnected

*edit* Here's another one. If your ISC has been shot for a while, there is a chance that the driver's in your ECU have fried themselves. Take a couple of minutes to pull your ECU to make sure that they're still OK. I was battling with this exact same problem for 6 months before I sucked it up and bought a new ECU and replaced the ISC with it. Now my car is remedied .

Here's what the driver shouldn't look like.

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[WatchItExplode]

I'm having the exact same problem right now, and I'll tell you how I (think I) solved it.

First I timed my engine to exactly 5 degrees BTDC (with the timing plug on the firewall grounded)

Then I started the car and let it warm up, idle was around 2000 rpm. I grounded the plug on the firewall and the plug under the dash so that I could set the base timing using the BISS screw. I turned the BISS screw all the way in and it only dropped 200 RPM. Turning it until it is completely closed is supposed to kill the engine. Because this did NOT kill my engine, it told me that the engine was still somehow getting air past the throttle body. I removed the throttle body and it was FULL of gunk from the EGR valve, causing it to not close completely. I cleaned it out really well and now it closes very nicely.

While I was at it I checked my ISC as described in the VFAQ and it checked out OK. Some people also report that leaky caps in the ECU can cause idle problems, but they seemed to be okay the last time I looked at them. Once I get my throttle body put back on I'll know for sure if the gunk was my problem.