2000 f250 5.4 2 valve,215,000 miles, California production. Lack of power on the top end so i changed the plugs and cop's. Fogged the throttle body. went to start and backfired, start again and stalls. MAF sensor is stuck at one value but no codes. MAF unplugged and value stays the same but loose the IAT. Short term fuel trims at 99.0. Can get to start if at least 50% throttle, runs really bad but runs. Pulled MAF sensor and tested on another 5.4 engine, it reads normal from what I can tell compared to the MAF on that engine. Pulled PCM connector and OHM harness, no shorts. Did a voltage test at the MAF harness with Key on engine off, got 12v at red wire to battery negative, tested black/white to battery positive got 9volt. At a loss, need new ideas.