New here, so be gentle! I bought a 1990 Convertible in July, 2017. Love the car and it has 62K on the odo. I had several Corvair convertibles and they were hot, noisy, and not very comfortable for long trips. The Reatta is smooth, quiet, responsive, rare, and gets a lot of attention.
Car had idle problems from the get go. Had an old retired tech put a new idle control motor on it and after a few heat cycles the erratic idle speeds came back. A friend and I bought a new tps sensor and pigtail. The old pigtail was in bad shape. We installed those and the car ran good because it was still warm. Got it home and the next start the idle was 2000 rpm. Re-started it and idle was 1500, then 1000, then back to 2000! On cold start sometimes it wouldn't idle without feathering the gas pedal.
Got to reading and testing the new and old TPS sensor and discovered the new pigtail was wired different than the original! Three wires on this TPS circuit, Grey, Blue, and Black. Went back to the store and showed them my old original pigtail and he looked it up on his computer and said it was wrong! He went to DelcoRemy site and showed me a picture of the new pigtail and it was different wiring from the original. The grey and the black wires were reversed. Said someone must have spliced in an incorrect pigtail.
I go back home and look and no, the connector was an original one! So, I rewired the terminal and plugged it in and instant steady, correct idle! Now, we have to set the TPS sensor so that it read approx. .5 volts at idle(has a CEL on when idling and showing code 22).
I learned: On my Reatta the pigtail is different from a standard GM TPS connector. Don't trust an original GM part. How to read codes with just a paperclip!
Thanks for reading my journey through a little mystery.