Rough/fast engine idle

meh_kick · **Posted:** Mon Jan 15, 2007 9:11 am

04 Renegade, 3.7 Auto, 72k miles (out of warranty)

I was driving on wet roads yesterday and the Jeep's driveline lurched as if I lost traction briefly. I didn't think much as I was on a slippery surface, but the check engine light came on shortly there after. When I parked the Jeep, it's idle was fast and rough. I shut it off and let it sit overnight. This morning it did more of the same. In park the idle speed is 1400 RPM and has periods of rough idle. In gear it runs at 1100 RPM.

I had an old plymouth do this to me once before, but to fix it I had to adjust a fast idle choke and all was well. I'm really not familiar with the Jeep's system to know what to check. I'd like some input before I take it to a mechanic.

I tried the key on/off/on/off/on to display error codes in the dash, but no luck. The guages just flipped.

Any thoughts?

meh_kick · **Posted:** Mon Jan 15, 2007 11:05 am

I've read a little bit online. My problem seems to be similar to others that have had a faulty Air Intake Sensor (AIS). This seems to make the computer increase idle speeds. Although this usually won't trigger the MIL.

I'm taking it to have the codes read now.

Anyone with thoughts please chime in.

callaway · **Posted:** Mon Jan 15, 2007 4:20 pm

mine (03 sport w/close to 50,000) has always seemed to idle rough. i never really gave it much thought that something might be wrong until now...

meh_kick · **Posted:** Mon Jan 15, 2007 7:50 pm

Local auto store read the code as PO122 Throttle Position Sensor A - circuit low. Which happens to be one of the codes read last time I had the Jeep in a dealer's shop for warranty work.

I brought it to a different dealer to look at it and offer their opinion hopefully the new work will fall under the previous shop.

(incidentally, other than the check engine light still on, the vehicle ran fine after sitting most of the morning...)

I will know more tomorrow.

LiLredLibby · **Posted:** Mon Jan 15, 2007 9:40 pm

hey meh_kick if you need some help with this problem and you want to you can PM me a phone number and I might be able to help ya. I'm pretty close to your neiborhood.

meh_kick · **Posted:** Sat Jan 20, 2007 9:08 am

If anyone is interested:

The dealer also read the PO122 fault code: Throttle Positioning Sensor Circuit Low and deduced that the sensor itself has failed (three months ago I lost an EVAP sensor).

So I'm out 50 for the part and my a## for labor... But all is running well, for now.

--Mitch

PS. Lilredlibby, I'm actually closer to West Middletown than the town of Somerville (my mailing address), so I'm really only a few minutes from Franklin. Did you say you work for a dealer up there or used to?

LiLredLibby · **Posted:** Sat Jan 20, 2007 4:45 pm

meh_kick wrote:

If anyone is interested:

The dealer also read the PO122 fault code: Throttle Positioning Sensor Circuit Low and deduced that the sensor itself has failed (three months ago I L.O.S.T. an EVAP sensor).

So I'm out 50 for the part and my a## for labor... But all is running well, for now.

--Mitch

PS. Lilredlibby, I'm actually closer to West Middletown than the town of Somerville (my mailing address), so I'm really only a few minutes from Franklin. Did you say you work for a dealer up there or used to?

No...it's an independent shop...Phils Auto and Tire. It's on RT 123 in downtown Carlisle. Our motto...We don't guess...We test. If you come here first you'll save money in the long run. :wink:

USPLibby · **Joined:** Thu Jul 28, 2005 12:29 am **Posts:** 377

I just had that sensor go out but I didn't really get a rough or fast idle just the check engine light. It was something like $43.00 at the parts counter and it took all of two minutes to install. Two torx screws, in and out.

Rough/fast engine idle

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