What would cause a 2001 F-150 4.2L idle rough?

get an obd2 scan to check for codes. many causes; tune-up, tps sensor, egr valve and dpfe sensor, o2 sensors etc... so get an engine diag.

-Switch spark plugs to factory motocraft plugs. Cheep and efficient! Also eliminates spark knocking with manual transmition and hitching or hesitation. Good Luck!