The truck was a 2000 ford f-150 with the 5.4L engine. What a PITA. The guy is deployed in iraq and I was fixing it for his wife. She thought something was wrong with the transmission because it was shuddering under load in the mid rpm range.
I found the problem after a few hours. The few hours wasn't the time it took to figure out what was wrong, It was literally how long it took to find the problem. The damn thing has individual coils over the spark plugs, and the fuel rail has to be removed to get to most of them, and the EGR valve has to be removed to get to some of them, and the intake has to be removed etc. It had the original plugs in it at 150k. Not only that but one of the damn coils was faulty, so it was running on 6. I changed the plugs, and re-assembled it, It was still idling rough, so I started pulling coil wires. Found a coil that when unplugged made no difference in the idle and moved it to the most accessable spot. re-assembled the engine and that coil still made no difference in idle when unplugged, So I replaced it, reset the codes, unplugged teh battery. hooked it all back up and started it up and the damn thing still idled rough. I went around and unplugged coil packs 3-4 at a time, noting that it took 3 seconds for the engine to smooth out a bit after I plugged one back in. I got all the way around the block to the last coil and plugged it back in and 3 seconds later poof, the miss was gone. Idling and running perfectly.
