My fathers F-150 with the 4.2L engine it had a hard time accelerating and misfired and has a real bad shake and rough idle. Ive replaced the coil pack, and the egr valve replaced the spark plugs. And that helped it up until yesterday it started back doing that all over again after 2 months of it running fine. I have pulled the egr valve out cleaned it put it back in and cleaned the MAC sensor. the cats have a rattle to it too. Anyone have any suggestions? i would appreciate it!

 

Check for codes before throwing any more $$$$ at it.

 

Yeah if the check engine light is on check codes first and I had the same problem with my cats so I cut them off it seems the 4.2 had problems with the cats breaking apart I know my truck idles funny but maf needs to be replaced and o2 sensors I hope you figure it out and post your finding