Good or Bad ISC

[Dr DSM]

is my ISC making normal motions?
good or bad ISC? - YouTube

I dont know if it needs replaced or not.

 

[kchaazz]

It comes on instantly when you start the car. I have all new gaskets and im running 25 to 20 lbs of vac while at an idle.

It comes on instantly, but does the light go off for a second when you rev the engine a little? I notice you have a 90. On my 90, I had the same issue you are currently having once. The problem ended up being the gasket for the throttle body where the throttle body meets the intake manifold. The problem is that the 90 gasket is much different from the 91+ gasket, and often the gasket is mistakenly replaced with the 91+ version, resulting in a massive vacuum leak. My car still pulled nice vacuum as well, but it just ran like junk. Ive attached a pic to illustrate...

 

[9!'clipseDOHC]

OP, your ISC in the video is moving correctly. If it also passed the ohms test, then I would say that it is good to go. If you think it may be an ECU issue then I would send it to the folks at ECMTuning. They know what they are doing and the turn around time is usually very fast. If there is a problem with your ECU, getting it fixed early can prevent additional damage. Even if it turns out that nothing is wrong, you will at least be able to rule that out.

how do you reset the isc?

There is no way to reset the ISC per say. I have read on here a few times (although I don't know if it is true or not) that once the ISC is adjusted it takes the ECU a while to "learn" it and that resetting the ECU (by unplugging the negative battery cable) will help it adjust faster. Personally I have never done this nor do I see the need. Once the ISC (and the ECU) is (are) confirmed to be working, follow the VFAQ to adjust your BISS: http://vfaq.com/mods/BISS-1G.html.

 

[92AWDTalonTSI]

We know one thing though... Eprom baby.

 

[92AWDHX40]

First are you having idle issues what else have you checked the isc is only part of the system.

 

[kchaazz]

There is no way to reset the ISC per say. I have read on here a few times (although I don't know if it is true or not) that once the ISC is adjusted it takes the ECU a while to "learn" it and that resetting the ECU (by unplugging the negative battery cable) will help it adjust faster. Personally I have never done this nor do I see the need. Once the ISC (and the ECU) is (are) confirmed to be working, follow the VFAQ to adjust your BISS: 1G BISS Adjustment.[/QUOTE]

A long time ago when I was having problems with this, Steve, on this site told me that when you adjust the biss via the instructions on VFAQ.com, the ISC becomes "centered" when you ground the timing plug and the plug in the diagnostic port- this could be considered resetting. Thing is, at least on the 1G car, the ECU has absolutley no feedback from the ISC as to the true position of the ISC and is always guessing. This is one of the reasons both the ISC and the ISC driver chip on the ECU go bad- when the idle cannot be brought down to the target speed, the ECU will just keep trying to extend the ISC over and over again, if that makes sense. So, in reality, much like doing any tuning on your car, you really should eliminate any vacuum leaks before attempting to adjust your idle after determining that you have a functioning ISC and driver.

 

[Dr DSM]

i got a good deal on an ISC so i went ahead and ordered one. I am going to try and get an ecu I found on craigslist tomorrow for $100 with eprom and socketed for dsmlink. I'll let you guys know if it fixes the problem. Oh and thanks alot for the help guys!

 

[bling5tatus]

Tonight I "fixed" broken ISC by taking the three screws off the back and twisting the shaft inside of it until the pintle was fully extended. It was about half way through it's range of motion when I removed it (not working) from the car. I made it go to the "full closed" position and reinstalled it in the throttle body. I did not plug in the harness connector to it. This sealed the leak it was causing my throttle body that my ecu couldn't control via the bad ISC. This will not yield a controllable idle from the ecu but it will fix a vacuum leak past the throttle body. If you're in a pinch this will stablize your idle until you can get a working ISC/ECU in the car.

For reference, before I did this my symptoms were unpredictable 1500-2000 rpm idle that would just hold steady and then sometimes it would come down to normal idle range and surge up +400rpms from there over and over and over. Blipping the throttle made the idle go high and stay there after your foot wasn't on the gas anymore. I hope that helps anyone that's as fed up as I was.