It would also be a good idea to check the fuel pressure when it's not running right. It might be a weak fuel pump.

 

I'll do the MAF first, then next will be to buy a fuel pressure tester...

 

any other low-cost tests I should do before I take it to a shop? Is there any way to test the MAF?

 

Started a new post (since clearly an engine problem) and posted a VIDEO!!!

https://www.ford-trucks.com/forums/1...ng-engine.html

 

Had the same problem,put new plugs and c.o.p.'s in it and problem cured and a drastic increase in gas mileage.2001 5.4 sd

 

turned out to be coils #2 and 4 failing under load then all the time. Fixed that, then overheated with oil in my coolant. Oil cooler failed and allowed oil into the coolant system. Bypassed oil cooler and back in biz...

 

On a 5.4L?

 

oil cooler is between filter and block... basically has heater hose running back from the bottom rad hose. silly system.