jayo310

Hey guys! This is my first post and I need some help. I bought my car a month ago knowing it needed work. But this is one thing I can't figure out, any suggestions are welcome! I've got a 99 cherokee, 4wd, 6cyl Automatic.

I'm getting some weird vibrations with my engine that's shaking my whole car, not a violent shake but very noticeable. The vibration is very rhythmic and the exhaust follows the rhythm. It's almost like a put put of a old choo-choo train. It only occurs on a cold start, and not so noticeable in the beginning after I start the engine. But builds up, and the vibrations get stronger as the engine gets warmer. If I put the car into drive or reverse, it stops. If I put it back in to park or neutral, it comes back. If I drive for about 10 minutes down the street, put it back into park, its significantly less noticeable and almost non-existent. I could see my RPMs jump around a little, but its mostly hanging around 700-750. And it drives great! Maybe the gas mileage is a little bit on the crappy side, but it seems ok.

I've also have had a P0301 come on and off which may or may not be related. I'm going to switch #1 fuel injector with another one, and same with the spark plug as a first step to diagnose the misfire.

Things that I have replaced:
Spark plugs and wires
Distributor
Exhaust Manifold (still need to re-check torque of the bolts)
IAC sensor
MAP sensor
O2 sensors
Air filter
Muffler

Maintenance:
Oil change with Marvel Mystery Oil
Transmission flush
Engine carbon clean
Cleaned throttle body

Any help would be greatly appreciated!!!