What causes an OBDII code on a 2003 Ford F-150 with a 6 cylinder and a 2wd?

Question

I have already done a tune up. I have changed the O2 sensors. The truck tends to shake when it is at a stop at times. For the most part runs good though. I just want to get the problem fixed.

Answer 1

Is the engine light (Service Engine Soon Light) ON? Are there any codes stored in the Engine Control Module (ECM)?  engine shake can be caused by bad spark plugs, coils or injectors.