dnaf150

2003 f150 4.2L, 128,000 miles has loss of power, engine rpms suddenly drops to less than 500, sometimes the engine just dies. No response to throttle (pressing accelerator pedal) when this happens. Started happening about 5 weeks ago about every 50 to 100 miles of driving with the interval decreasing to the point the engine would start and then immediately die. 3 weeks ago I took it to the Ford dealer because of really bad hesitation on acceleration. Ford dealer detected bad manifold gaskets and changed upper/lower intake manifold gaskets which greatly improved acceleration, but I returned it because there was still a little hesitation on hard acceleration. Dealer recommended new coil pack, plugs and wires, I told them no thanks and drove the truck with no major issues except the loss of power sometime, which became more frequent to the point I couldn't drive it. Then I replaced the coil pack, plugs, wires and also the fuel filter and still would only start and immediately die. Next I changed the fuel pump. Started and died about 8 times and then ran okay, drove about 15 miles, parked it and the next day it would start and then rpms dropped below 500, no response to throttle inputs, then it would respond once or twice and then below 500 rpms again.

Towed it to Ford, check engine light has not been on since before I took it to the dealer. Mechanic said fuel pressure was 40psi when engine was running fine and also when engine would lose power, rpms drop below 500. They have had it for 3 days and cannot find the problem. Any thoughts on what it may be?

SixShooter14

It could be a few things. Top of the list to check would be:

Idle Air Control Valve
MAF Sensor
Throttle position sensor