High idle speed and trying to shift while at highway speeds - Grand Cherokee


2004 Grand Cherokee. I was pulling a heavy trailer 1000 miles, and while coming down a mountain pass 50 miles from the end of the trip the check engine light came on. All other gauges (oil pressure, temperature, etc.) had not changed while climbing or descending and I was in low gear while descending to save the brakes. I drove the rest of the way to the destination without incident. I tried turning the Jeep off and restarting it several times to see if the check engine light would turn off and it stayed on. The next morning the light was off when I restarted it and has not come on again since. I hooked it up to a scan tool and received 2 codes: P0152 and P0132. 2 days later I noticed that it was revving high while idling and in Park. It would rev between 1500 and 2200 RPM while in Park, and at 900 RPM while in Drive. Also, while travelling at freeway speeds it seems like it's trying to downshift for no apparent reason. I hold the throttle still and have even tried cruise control and it intermittently increases engine speed, without changing ground speed. I assumed that I got the transmission too hot while climbing/descending and that the error codes listed above (related to O2 sensors) were associated with that, but now I'm wondering if something more has happened.


From ODB Codes

P0132 O2 Sensor Circuit High Voltage (Bank I Sensor 1)
P0152 O2 Sensor Circuit High Voltage (Bank 2 Sensor 1)

Since I’m not the ODB guy, I can only guess. You’ll get a better input below, I’m sure. But I believe they’re related, and a single component is causing the problem. Possibly the MAF needs to be cleaned, and is causing an excess in fuel to be delivered. Don’t take that as anywhere near gospel, though.