I own a 97 F-150 4.6 The problem started with the motor losing a cylinder here and there. Dealer states needs plugs and wires which I replaced on my own. Problem still existed, now with check engine light flashing. Played around with wires and had code reset by local mechanic. Replaced fuel filter, replaced both coil packs, fuel pressure is fine, ran several bottles of fuel injector cleaner thru tank and checked to make sure heater hose was clamped avoiding any anti-freeze leakage into plug hole. The only thing that I havent done is had the injectors cleaned professionally. The check engine light has been on for a few weeks now, and had received an indication that the engine was running lean, we reset code and the light came right back on and has been on since. Getting about 11 mpg and it mainly stumbles on take off and at lower speeds. Please help its been about 7 months and still no fix. Trying to avoid paying the dealer an arm and a leg.

 

have you checked the oxygen sensors??????

 

I had a '99 5.4L with the same symptoms. Missed at idle. Had a little bit of a driveability problem from a stop. Was fine on the highway. Gas mileage slowly decreased with a worsening of the missing and driveability problem. No CEL light. Finally, one day, engine was barely able to idle and the CEL started to flash and by the time I reached the dealer, the CEL was fully on.

Turns out the IAC was bad. Dealer replaced it and problem solved. Gas mileage went back up too.