last time my challenger had that symptom or it would kick the engine over for a second on key release it was ecu...always good idea to carry a spare ecu anyways...one way to do a quick test it is to just turn ign. on unplug dist connector,,and on the harness side the male terminal just touch it to ground for a second you should hear it spark every time you ground it...if it sparks problem probably in dist,,,if it doesnt spark then problem is in the car,,had a bad dist connector on harness side once even though it looked good it wasnt...