Changed oil and now runs rough

[JuststrokeIT]

I have a Buddy who changed his oil the other day says the truck ran fine before. But afterwards the truck runs really rough at idle and had low power and barely wanted to move but one it warmed up it had power but the idle was still really rough.he told me he had to break the old filter off to get it out of the cap n put a motorcraft one in. So I told him to go buy a new cap from for since i know most aftermarket filters and caps are one time use. He says he changed that out and now it has plenty of power but the idle still sucks where should he look next? I havent seen this truck before so i really dont know to much about it