I am suspecting a bad ISC on my 89 SOHC 2.0 Galant. I have a spare one from a 91-93 Turbo DSM. Are they the same?

I wouldn't think so, since for DSM's the 90 ISC is different from the 91+.

Rafal, if the old (89) ISC works the same way, you should at least be able to test it to make sure it's good. Google should help you find something like this: http://www.geocities.com/MotorCity/Downs/7678/dsmtests.html

At the least, you can test your 91 ISC to see if it's good, and then offer it in the For Sale section if it's not compatible with the 89.

Thanks guys. The ISC on the Galant is in fact completely different.

The reason I suspect a bad ISC is because (after searching the forum and finding people disconnect the darn thing) I noticed that when I disconnected the ICS when the car was idling fine, my surge, low idle, CEL problems have gone away. We'll see if this is a good cheap fix, I haven't driven the car much since the disconnect.

I haven't taken a multi meter to it yet to test the resistance between terminals, but does my diagnosis sound ok based on the above?

Is there any harm in running with the ICS disconnected (other than having to manually keep the revs up when cold?)

Nope!

Thanks Rob.

Just hope this fixes it, I like cheap fixes.