My erratic idling problems when the engine warms up was traced back to the computer. Do I need to find one of the exact same year or are they somewhat interchangeable? What should I look for? Thanks.

 

As long as you get the same GM part no, for the ecm you're OK, as long as you swap the two calibration chips from your old one into your new one. You need to remove two 1/4" hex bolts to access the calibration chips. They only plug in one way.

 

What Grumpy says. The '88 is a one year only ECM in the f-body and another year or two in some 4.3l's elsewhere. It may be hard to find (1228063). If found just swap parts as above.

The '89-'92 f-body's and '89-91(?) Caprices used the 1228746 ECM. Better code and more readily available. The difference is that if you get one of these then you must either match the car/drivetrain of the donor to yours, or purchase the correct MEMCAL that matches your vehicle.

Best to check which is in yours first as it may already have been changed out.

RBob.