I have a 4.2L 2002 F150. At low RPMS it runs very rough. Once I get to around 60mph it smooths out. I have changed the plugs and the air intake valve. Niether of these seemed to be the problem. Any suggestions on what the problem may be?

 

Check for codes.

 

I checked the codes and have 2 cylinders miss firing. Put new plugs in and cleaned the MAF properly and also changed the fuel filter. None of these have helped at all. My truck has 293,000 miles and has run like a champ up till now. Does the MAF sensor just go completly out or can it work some what? Any more suggestions? Please I need some help. go

 

Coil pack had the same problem.

 

Thank you I will try that. DO you happen to know if the coil pack can be partially bad and still spark?

 

Yes mine had a weak spark it would still run it would go away when i had 2000 rpm but at take off felt like it was not firing.