I've had this problem with a car I'm working on for a while now and I cant figure it out. It backfires and sputters anytime the accelerator is pushed down more than about half way. If you give it 25% throttle, it will rev smoothly to redline. If you give it 50% or more, it will just sputter and backfire really bad. I've tried using new MAP, TPS, IAC, Air Temp, and throttle bodies off of another FD and nothing worked. I've disabled the secondary butterflies, adjusted the TPS, dash pot, and idle stop screws. Nothing worked. I replaced the ECU... and it worked fine. UNTIL I shut the car off, and then re-start it, and problem comes back. If I put in the old ECU, it will run good again until I shut it off again, then after restarting, the problem will be back. Any ideas?