My 5.4 has 140,100 miles. It starts easy but I have a rough idle after starting with a cold engine. If I rev the engine up to 2K rpm 4 to 5 times, it idles and runs smoothly. If I let it continue to idle rough, my service engine soon lights up and stays on after revving the engine and runs smoothly. The service engine soon light stays on till I disconnect the battery. The engine runs fine after revving it and the service engine soon doesn't light up. I replaced the fuel pump about a 1000 miles ago. It started the rough idle about 250 miles ago. All the coils and spark plugs were replaced about 5000 miles ago. Fuel filter about 5000 miles ago. Engine does not leak oil or coolant.

 

Does it run rough while it's cold and runs good when it's warm?? Mine was doing that and it ended up bein intake gaskets. Take a can of throttle body cleaner when it's cold and running rough and spray it all around upper and lower intake gaskets if the idle changes that's it.

 

Yes. It runs rough cold and runs good warm. I'll try the intake spray. Thanks!

 

Oh yeah, my intake manifold was replaced w/ gaskets 3000 miles ago due to coolant leak.

 

Double check your wires and plugs, cause you have coils, plugs, and wires, if their oem wires Id change them, and do a decarb since you have the same problem I had about 5000 miles ago (same mileage your at now) I would take off your air box, filter, and take intake/throttle body cleaner and clean up the throat area, also try some seafoam 1/2 gas tank, 1/2 in the brake booster Dont hydro lock your engine though lol, and lastly check your EGR probably has a **** ton of build up! Comment back when you figure out if that all fixes it!