Rough Idle, Vibration at Highway Speed
I have a 2001 Jeep Cherokee Sport that is having some issues. There is a miss at idle, causing a rough idle. When I get on the highway, once I hit 70MPH I start getting a vibration. If I accelerate up to 75 and back off, as soon as I get out of the throttle the vibration is gone, until I get on the throttle again.
Last year, I had the Intake system cleaned, and it ran GREAT after that. I also replaced the plugs. The engine has 125,000 miles on it. I inherited this from my mother, and IIRC she started having the same problem after a trip to Alaska, when they drove through Canada. Her mechanic thought it had something to do with Canadian gas. I tried different grades from 87 to 93 octane and it makes no difference.
The engine is stock with the exception of a K&N Cold Air intake and filter. The suspension is all new (shocks, leaf springs, bearings) and the tires are new Michelin LTX Touring tires. I don't think this is suspension related because when I back off the gas the vibration stops, so it seems that it is related to the engine load.
I am still looking through my mothers paperwork to find out what maintenance has been done on it. Any suggestions on this problem are welcome!