I have a 1993 F150 5.0 2WD Automatic Transmission Ford truck. I am exasperated with this problem and cannot figure out the problem. Idle is fine for awhile and then slows after engine warm.
Main problem is after engine warm, when it shifts 3rd and 4th gear it hesitates, shakes until i push down gas. Each thing I’ve replaced has made it better for awhile. I’ve replaced : distributor cap, rotor , fuel filter , spark plugs & wires , map sensor.
Also 1 Oxygen sensor, I’ve found online that there is supposed to be 2 , but only found 1 and replaced that. When I first leave in morning with it it runs and shifts great until engine gets to normal temps. Please Help !!
I think I would start with checking the fuel pump pressure with a manual fuel pressure gauge. You can rent the gauge from your local auto parts store, or have your mechanic check it for you. You might also want to clean the throttle body and the idle speed control motor.
When these items get dirty they will cause erratic idle, idle speeds which are too low and dying at idle complaints…although they will NOT produce the 3rd and 4th gear complaint you have, but lack of fuel pressure will. Ford trucks are notorious for bad fuel pumps, and fuel pumps tend to fail most when they get HOT.