I have a 1994 sc400 which dies when decelerating(but not all the time).The IAC valve,fuel tank,pump,filter,battgery,wiring,altenator are all new.The computer has been rebuilt and rechecked(solved the problem for 2 weeks),throttle body cleaned-I give up-any thoughts?
Vacuum leak? Intake manifold gaskets. All vacuum lines?
Since the computer rebuild affected this problem, but then it came back, I’d expect the ECM is getting faulty feedback from some engine component or the other. Possibilities include O2 sensors, MAF, IAT, etc. If you can find someone to do an emissions test, that might be helpful in determining whether the fuel/air mixture is a problem.
When you decel, with the car in gear, the ECM normally cuts off all fuel to the injectors. A fuel saving feature. But it is supposed to start injecting fuel again when the car slows to a certain speed, to avoid stalling. You might try doing some decels as an experiment with the car in neutral, just using the brakes, see if that has any effect. It may be the ECM is forgetting to start injecting fuel again.