I got a tip from a fellow that had heard of the problem several years ago. The O2 harness wire pin positions are critical. I replaced the harness with a new one that was supposed to be correctly configured for a '89 5 speed. Looking at the old and new O2 harness connectors there is one wire positioned oppositely.
A repinning of the new connector this weekend to mirror the old one and we'll see if that does the trick. I just love electrical problems - I live for this!
