rough idle, bucking -

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post #1 of 2 Old 06-25-2012, 04:06 PM Thread Starter
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2000 XJ Cherokee 
Join Date: Feb 2010
Location: Long Island
Posts: 9
rough idle, bucking

driving home from the beach the other day i was traveling about 65 mph, i let off the gas entireley as i was approaching the off ramp, and my RPMs went from the 2000-2200 range down to about 1750, right back up to the 2k range, and back down (CEL came on at this time). I decide to drive it to the local auto parts store to have the code read. driving on a road with a speed limit of 40, there was no "bucking" or abnormal fluctuations in the RPMs. as soon as i put the jeep in park, the rpms jumped to 1500, while they normally sit a 750. Finally had the code read. P121, P122, and P123 came back. I had the code cleared, and cleaned out the throttle body and the IAC with some CRC cleaner, thinking it would resolve my issue. After cleaning all the gunk out, it idled normal again! i took if for a drive and the bucking/surge in the RPMS was nowhere as severe, it felt like a small jerk after letting off the gas. driving 50mph, let off the gas, and the RPMs dropped a tad and went right back up, but certainly noticeable. after all my reading and research, everything seemed to point to the IAC, TPS, MAP, etc, so i cleaned them out. The CEL just came back on, i feel so lost. any input is much appreciated. :

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post #2 of 2 Old 06-25-2012, 05:34 PM
It's the crank sensor!
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1999 XJ Cherokee 
Join Date: Nov 2007
Location: Central Minnesota
Posts: 8,755
Always, always follow where the codes point you to.

All three of them are for your throttle position sensor.

Replace it with one from either Jeep or Napa if you choose aftermarket. This sensor cannot be cleaned. Do NOT buy any cheap charlie engine management sensors; lots of Chinese stuff floating around that is absolute crap.

The part is not that inexpensive and it's easy to change. Plug and play.

Good luck and keep us updated if this resolves it.

99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!
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bucking , cherokee , rough idle , rpms

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