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I drive a '99 Wrangler 2.5 L 4 cyl 5 speed and been having "bucking" problems with it for quite some time now and cannot get to the bottom of this. I replaced the O2 sensor about a month ago and it fixed the problem for awhile but now the Check Engine light is back on and the 'bucking' is back again. I get the bucking to stop when I either let off the gas or hammer down. I notice it really gets bad when I'm going over bumpy roads and when the jeep is warmed up. Also, it starts to cut out sometimes when it's idling but never enough to make the jeep stop running.

The codes that came up are:
- P0171 Fuel System Bank One Sensor One
- P0133 O2 Sensor

My mechanic suggests I get rid of or replace the cat converter and in my case I'd rather get rid of the converter and not spend the extra money.


Some solutions mentioned in this forum were:
- Plug wire arcing to the head where hidden behind the A/C compressor
- Take IAC & TPS off the throttle body, clean IAC, replace TPS
- Crank Position Sensor
- Airbag Clock Spring
 

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Omg! Are you secretly driving MY jeep? I'm having same issues. I removed the cat, but still runs like crap! It seems to be a VERY common problem, but no one can say, "hey, dummy, here's your problem". It's SO frustrating!!!! I'll keep watch on this thread. Maybe someone will have a REAL solution......
 

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I had the same problem guys. Upstream O2 sensor. Stay away from Bosch for sure but the OE brand (escapes me right now) is available at part shops. A wrench and 5 minutes will fix it. By the way if you get caught getting "rid" of that cat you won't like the fine.
 

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Imma hafta wait til Saturday to work on mine. If ya get it on before then, post up how it worked for ya. My fingers are crossed for ya.
 

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It is threaded into the exhaust pipe close to where the pipe is bolted to the exhaust manifold. Make sure to use anti seize when you install the new one
 

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Thanks! Any other suggestions to look at/try, just in case that isn't the culprit? Kind of a "plan B"...... Remember, I'm mechanically challenged.
 

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I've had the bucking problems with my 99 TJ 4.0 as well. Once it was the O2 sensors (there are 2 if you can afford it replace both) and once was a plugs, cap, wires and rotor replacement which did the trick.
 

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Well.....I replaced the upstream o2 sensor. Ta-daaahhhh!!!! So far, the jeep is running like a sewing machine. Thanks to all, for the input.
 
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