1998 Ford F150 4X4 automatic with 5.4 distributorless ignition system. Milage is 104,000.
At about 90,000 began a slight missing, especially under load in lower rpm of overdrive gear.
Mechanic found a faulty coil on cylinder 4. And he replaced all plugs. Ran smooth a while, then missing returned. I happened to change air filter, and missing was gone a long time. Then it returned. One day would not idle correctrly and mechanic found code saying " Idle Air Control" unit bad and it was replaced. But they also did carbon clean out and clean out of air intake. Then it ran its very best with no missing and great power for 300 miles. Then in heavy snow storm and 23 degrees outside, it began severe missing and engine light came on. Codes said was missing at 1600 rpm and 37 mph but did not say a specific cause or cylinder. Mechanic replaced coils and plugs on cylinders 7 and 8. He also replace transmission fluid (he has a theory it is the torque converter, but that makes no sense to me)
Missing is now back to the old minor problem that has been there for 10,000 miles. Your other articles make me wonder about 1) fuel pressure regulator 2) EGR (but I checked that valve and it is quite clean and works easily) 4) fuel injectors or maybe 5) oxygen senson. Wonder if you could point me in a more specific directon. Going nuts here. Need to keep the truck. Thanks