Hesitation and bucking during acceleration

My 1999 xj has developed the following problem.
While accelerating there is a bucking/hesitation that feels similar to hitting a bump in the road.l would appreciate any help diagnosing this issue.
4.0 with 186k

does it "pop " ? Mines doing something similar, and includes backfiring through the intake. Only does it upon start up for about 5 minutes then runs fine the rest of the time, but if I shut it off to go in a store it does it again.
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If it only does it when cold or after maybe 2-3 minutes after start up, I'd look at the O2 sensor.

My 96 was popping and bucking about 2 minutes after start up, it would mostly go away after the motor warmed up some. It turned out to to be the front O2 sensor. Checking the O2 sensor heater fuse is also a good idea.

I'd check the codes, a failing TPS sensor will usually show up, a failing O2 sensor may not.

HAPPY.DOG said:

does it "pop " ? Mines doing something similar, and includes backfiring through the intake. Only does it upon start up for about 5 minutes then runs fine the rest of the time, but if I shut it off to go in a store it does it again.
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No popping or backfiring.

8Mud said:

If it only does it when cold or after maybe 2-3 minutes after start up, I'd look at the O2 sensor.

My 96 was popping and bucking about 2 minutes after start up, it would mostly go away after the motor warmed up some. It turned out to to be the front O2 sensor. Checking the O2 sensor heater fuse is also a good idea.

I'd check the codes, a failing TPS sensor will usually show up, a failing O2 sensor may not.

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Pulled the codes and it's a.P0455, major leak in purge control system.

I drove 2.5 hours today on yhe high way and it did it intermittently the entire trip.

O2 sensor circuit is a likely suspect, so is the Throttle Position Sensor and the Coolant Temperature Sensor. Inspect the wires, inspect the wire plug pins, test the sensors. O2 sensor have a service life of about 100-150,000 miles and are routine maintenance.

Only buy genuine Jeep engine sensors and NTK brand O2 sensors.

Tim_MN said:

Only buy genuine Jeep engine sensors and NTK brand O2 sensors.

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+1

I recently replaced a local parts house TPS with Mopar TPS. I was having multiple problems with mine including missing, hesitation, bucking, rough, low, high & hunting idle and transmission shifting issues. Most of this would clear up when it warmed up. No codes ever showed up and decided to do the change on the chance it would work. It cured everything but the low idle and I just found out that was caused by a clogged fuel system.

Luckily I didn't burn it to the ground as the regulator was poring fuel directly on the header after the seal blew out at 70mph on the highway.:wow:

I am changing the CTS today and will try the TPS if that doesn't work.

I changed the CTS with no luck. I also tested the fuel pressure which was 47 or so at idle so I think my next step is the TPS when I get paid.