Start up problems...(4.2L v6)
Whenever I start my truck and the engine is cold, whether I am sitting in park or whether I start driving, when the engine gets to an idle, the RPM's will slowly drop from around 1000 down to around 6-700 (which is normal) but before it gets down to regular running rpms, the engine seems to shudder and the RPM gauge will go up and then drop and up then drop and shake. If you give it gas the engine revs smoothly. I already replaced all the plugs when I bought the truck in March with the Motor craft plugs. Could this be a Coil Pack going out?