Well it's good that we solved that riddle. Keep us posted on your progress!

P.S. I'm not sure how the MAF is configured on your '90 2.3L, and whether or not is capable of being cleaned, but cleaning the MAF sensor is one of the things people do to help get rid of the pinging, at least on the Ford 3.0Ls and 4.0Ls. Here is a link to another thread on the subject of Throttle Body/MAF cleaning:

https://www.ford-trucks.com/forums/s...hreadid=116328

Like I said, I'm not sure if it would apply to your 2.3L setup or not.