I wanted to keep my ISC so I used the "jb weld" method of blocking off the FIAV. After getting the 5 screws out (I used an impact driver and still stripped two) pop the freeze plug out by hitting it a couple times.
The ISC does this as a stepper motor under control of the ECU, which can finetune the idle rpm. The Fast Idle Air Valve does this as a very coarse adjustment based on temperature.
The ISC does its job well, and fixing something thats not broken, is your decision. The ( 2 ) that I know work are the: 1990 tb- off a 1g talon/eclipse/laser & 1991 tb- off a Galant VR4 or 1gb Talon/eclipse/laser. I run a ISC with no FIAV. Works well for me. And if it ever was to break. I would probably buy a ISC/FIAV blockoff plate.
For the original ISC (silver body with brown socket), values measured between pins 1&2, 2&3, 4&5 and 5&6 should be 28-33 ohms. The newer (black) ISCs should measure about 40 ohms across those same pin combinations.
You want the ISC in the middle of it's range, while adjusting the BISS for optimal setting (Our idle should be 800 RPMs). But what exactly is the middle of it's range? If you log it, I think it goes anywhere from 0-100+. Does anybody have hard evidence on where it should properly be set @ idle with a logger using MMCD?
I have been having issues with idle and stumbling and/or stalling, so I checked the ISC. The only test I could find online was for a non turbo, but they said it should test 28-33 ohms between pins. I got 36 ohms on all pins. Now, is it out of spec or do the turbo cars test out that way. Also...