came on quite suddenly, kid been starting engine w/o pushing in clutch,thought maybe it jumped time, but underhood sticker says timing not adjustable, idle speed/mix also non adjustable. truck sat for 5-6 years, then was "refurbished" by so-so mechanic....ran ok for about 3 months. has new fuel fliter, we changed alot of vacuum lines, checked vacuum motors in air cleaner, shot pb blaster into egr...