IDLE SURGE- New ISC moves opposite to old ISC

[Demon33]

Have any of you fellow 1990 4G63T owners successfully replaced your '90 ISC (with pigtail connector) with the newer version of ISC (without pigtail connector) and didn't experience idle surge? After A LOT of testing and troubleshooting, I'm convinced the new ISC is the source of my current idle surge.

My old ISC wasn't dead but I recently installed a newer ISC in my '90 throttle body in hopes of putting less load on my 20 year-old ISC drivers and hopefully extening their life a little. Since making the change I have been experiencing bad idle surge. In my search for the cause I did a boost leak test and fixed a leaking EGR valve. No other leaks exist, but the surge persists. Base ignition timing is 5 degrees BTDC, BISS and TPS are adjusted properly and idle switch is set and working.

After extending the ISC wires on the harness, I tested the new ISC by plugging it in and turning the key to the ON position and the pintle (tip of ISC) moved out and extended from the ISC and made clicking noises for a bit. The position shown on my logger is about 108. When I turn the key to the OFF position the ISC pintle moves in or retracts a little and the logger shows 90 for the position. As the car warms up, the ISC position begins to move towards 0 (ISC fully retracted) which allows more and more air to bypass the throttle plate. This has the affect or raising the idle RPM which leads to idle suge.

However, tonight when I plugged my old ISC back in and turned the key to ON the pintle retracted which is completely opposite to what the new ISC is doing. When I turned the key to OFF it extended slightly.

I'll probably reinstall the old ISC tomorrow, but I just need you guys to verify whether or not you've been able to use a newer version ISC in place of your '90 ISC without any problems. If you have, my new ISC might be defective or I may have just wasted my money.

 

[josh38127]

I was told by a few people that it wouldnt work. you can swap any isc from any other 1990 car

 

[D@nno]

I'm having the exact same problem, did putting in the original isc fix the surge?

 

[Demon33]

Ya, I put the original '90 ISC back in and it's working perfectly. Haven't had a problem with it since.

 

[VisionPaintball]

Ya, I put the original '90 ISC back in and it's working perfectly. Haven't had a problem with it since.

damn i just went through this same exact thing. I couldnt get my car to idle steady at all so i tried the 90 isc this morning and now its prefect.

 

[D@nno]

I found a good 90 isc at the wrecker and now the car idles good! The 90's must be wired differently at the isc, the wires are the same up to the connector.

 

[steve]

When you did the wiring, did you just copy the wire colors or did you check to make sure that the pins from the ECU went to the correct pins on the ISC?

 

[VisionPaintball]

When I did mine I just copied the color of the wires, not the ecu pinouts. I guess that's the problem?

 

[Wrenchit]

I tried to relpace my ISC with one out of a hyundai motor's, but the plastic covering was too big even though it had the same shape. The new ISC I had was alot better at controlling my idle though.