1985 Toyota Supra LOW IDLE. ECU PROBLEM?

(rebuilt.I think)

I recently bought 85 Supra.(NOT TURBO) :( Worked great first 3 months, then just died one day. Battery and starter was fine just wouldn't turn over. I replaced dist. Cap & rotor and it started but would not stay started in gear (ok in park). Cleaned out throttle body and is working ok but in gear idle is 500 and really engine really wants to quit. This year of Supra the idle cannot be adjusted, found out it is controlled by ECU. I am a novice @ some car repairs. Got any ideas? THANX SO MUCH. I love my little car.