2000 f150 with 4.2 v6 started miss firing at idle. It has a 5 speed manual transmission and all though it will run for several minutes while stopped it will stall while in motion at low Rpm. Most of time while stopped if I crank it the Rpm will go extremely high and it will only come back down after around 10 to 15 seconds, tapping the excelerator doesn't seem to control Rpm when it's doing this. Highway speeds you wouldn't know there was any problems. Thanks for any advice.