Hi so I have a stock 99 sport 4.0 6cyl 5 speed. After driving for about 30 minutes and warming the engine up I get a rough idle and vibrations that I can feel through the driver's seat and floor. The rough idling and vibrations seem to come in waves. I replaced spark plugs, coils, and distributor recently and double-checked all the connections. Is this a clear case of the hot soak issue or could it be something else?

 

Heat soak is more when you try to restart the (hot) engine.

Rough idle and vibrations, with that combination I'd check for misfires. Rough idle itself can be a few things.

Any codes coming up?

 

Thanks Roler I am going to check codes today and also do a fuel pressure test. Anything else I should check out? Throttle body and sensors? It seems to run fine on initial start up but after it's at temp is when the idle and acceleration issues start.

 

Ever changed plugs, wires, cap and rotor?

 

Yep I just changed plugs, wires, cap, and rotor about a week ago. I rechecked all the connections and firing order and that all looks good. It really only seems to have the issue after highway driving. It runs and idles fine around town but after 15 min or so on the highway and coming to idle or accelerating is when it idles rough and has weak acceleration. I just passed an emissions test with it if that makes any difference. At this point I'm thinking maybe fuel injectors or fuel pump?

 

Oh so it's acceleration too?
thought only idle issues and vibration (at idle)