Engine or gearbox
 

Recently my 2002 4.2 Coupe has taken to revving up and down slightly on light throttle openings, for instance at 30mph. It also appears to change up and down a gear. Could this be engine or gearbox problems? Also having drawn a blank trying to find a security module either new or secondhand,does anyone repair these? :icon_nut:

Could as easily be a split or loose (vacuum) hose. Go hunting or find an expert.