Thank you for all the responses!
I thought I looked pretty thoroughly, but will try again.
I just picked up the car (539) from Arkansas and drove it home to Chicago. The car was running slightly rough when I picked it up, but 100 miles in to ~700 mile trip it started to misfire badly with the check engine light periodically coming on. It limped the rest of the way home.
I had no choice, but to drive it the rest of the way, hopefully no damage resulted from that.
Another thing I noticed was the oil pressure gauge being always pegged to the max in the lower gears.
Currently my ZR1 has the power of a poorly tuned Chevette.
I found couple of vacuum hoses loose (MAP and pressure regulator), I also replaced PCV check valve assembly hoses with ones from jerrygaskets. It and the felt much better at first, but after a short test drive it reverted back to a bad misfire and shake.
So this is where I am now…
So ’91 ZR1 has a 12 pin ODB1 connector?
This one right?
https://www.moates.net/aldu1-and-cab....html?cPath=64
Thanks again!