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1G 91 ISC in 90, looking for the ecu pinouts between 90/91

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Tyeler18

15+ Year Contributor
2,491
242
Dec 16, 2008
Casa Grande, Arizona
All 3 of my 90s all have idle problems. Each ones running a 91+ TB with matching sensors and they all surge.

I was reading a post by Steve, which I can't seem to find, that was saying the wiring is different between the 90/91+ ISCs but can't find a pinout to confirm that.

Currently my ISCs are all still stock wiring, they're just plugged in off the main harness just like a 91+ is. Anyone have any insight or a pinout to confirm the actual wiring to the ecu is different?

With link plugged in my ISC will sit at 120 steps, then when it's started it'll slowly decrease until its at 0 steps and is impossible to get to anything other than 0.
 
I just found this problem last night. I was working on a 1990 talon and it has a 91-94 throttle body and when the IAC is plugged in the car idles very high. After checking everything out turns out the ISC is working backwards. So i need to find out what pins need to be switched.
 
I am in the process of doing the same thing with my 90, using a 91+ N/T throttle body. From looking at the pin outs from 90, and 91+ all are the same with the exception of pins 6 and 14. But...if you look at the ISC connector plug itself between the 90, and 91+, the white wire and black wires are in switched positions. So, I believe that instead of swapping the pins at the ecu, you will have to swap the white wire to the black wire at the plug, and the black wire to the white wire at the plug. Again, This is my assumption because I am not around my car and have not got everything installed on my car yet but when I was researching for myself that was the conclusion I came to.
 
I just switched the pins on the IAC plug. The lower row left and right side need to be switched. So you are correct the black and white need to be swapped. Everything is good now idle is perfect.
 
Nice work, guys. I assumed it was the same on the '90 harness and never revisited to make sure. My article points out my error and links to this thread.
 
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