Sounds like they need to pull the harness and go through it with a volt/ohm meter, and check to see if there is a cracked or bad wire. Check all the grounds, and what did they do for a dash? Did they rewire it to the 85 wiring, or just use the dash wiring from the taco? Could be causing feedback into the ECM. Maybe it's time to take it back to the toyota mechanic.
