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Q: why would my jeep be bucking and jumping intermently? on 2001 Jeep Wrangler

It's parked in garage overnight and in the mornings starting up it sputter's and then as I start to drive it starts bucking. I've had a tune-up, serpentine belt had crack and was replaced, had throttle positioning sensor replaced and still bucking. Had induction cleaning, no change. Tried changing out map sensor and that didn't work so took back off. Voltage on wiring checked and no voltage lost. They put the diagnostic reader on it and pretty much tried checking and changing everything the codes said to check and still nothing changed. The strange thing is that it's not happening all the time the last place we took it to thought two different times that they had fixed it because they took it for a test drive and it drove great the next morning I picked it up and took it for a test drive and it started bucking so we pulled it right back into the garage. They checked a few other things and we test drove again and it appeared to be fixed I left on my way home and about 3 miles into the drive it started bucking again so I turned around and took it back. That's when they checked the wiring thinking it may have a short. After checking it over once more I got the phone call saying they couldn't find the problem. We went and picked it up and it drove fine on the way home. Parked for about 30 min. drove to store everything was fine. Parked overnight drove to work 25 miles next morning no problems and 25 miles home still no problems. Parked again overnight got up this morning and started driving and it started bucking again and bucked all the way to work and on the way home also the check engine light came back on. We are at a loss as to what it could be. Anyone have any suggestions? Any help would be greatly appreciated!!
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As with any Intermittent problems Basics need to be covered. Fuel pressure and Volume need to be Inspected for a weak Fuel Pump. As you mentioned Tune up was performed eliminating Ignition misfire. Crankshaft Sensor could have a loss of magnetic pick up causing random cylinder misfire.
Check the wiring for the oxygen sensor. I had a similar problem with my Jeep. The oxygen sensor is located on the exhaust header near the junction with the front end of the exhaust pipe. The sensor has 4 thin wires that are covered by a mesh protective cover. On my jeep, the cover was pushed up, allowing the wire insulation to rub on directly on another surface. Eventually the insulation wore down and shorted out the sensor. Inspect the wiring from the oxygen sensor to where it plugs into the wiring harness. The problem would first occur occasionally, and became more frequent as the wiring deteriorated further.

A replacement Oxygen sensor costs about $45 at Autozone.

Good Luck.

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