I have just bought a 1997 f150 extended cab. I have noticed that when i first start the truck it has a slight vibration that comes and goes when the truck is idling. If you step on the gas it will go away. If you turn the steering wheel it will sometimes go away. The vibration does go away when the engine warms up. Truck runs fine. Good oil pressure, no knocks or pings. What do you guys think?

 

mine too, there is a number of threads on rough idle - mine has done it for aslong as i can remember - it can also be caused if your oil level is too high so dont overfill the oil - i generally keep mine at about the 3/4 mark of the dipstick

 

Local Ford dealer here claims rough idle can be caused by wrong weight oil!!!!!!!!!!!!!!!!!!
I make no claim to truth here, I only pass along this pearl of wisdom!