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Afternoon,

Been fighting an issue for a couple of days now with my 03 Durango with a 4.7 engine. The P0121 code came up a couple of nights ago and it began running rough and having difficulty idling. It also has quite a pause in accelerating from a stop light. Occasionally, my cruise control won't turn on either.

I have installed and tested a new TPS and a new MAP sensor with both checking out with my DVOM. Installed a new gas cap since the old one was damaged, just in case that would do it. Changed one vacuum hose with a crack in it from the Purge Valve Solenoid to the Throttle Body. Still running poorly as listed above. I'm not much of a mechanic so I'm not sure where to go next. I have read the P0121 posts here but not finding anything new. Any help would be appreciated. Thanks.
 

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inspect and reseat the PCM connectors.
 

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Unplugged the PCM connectors today and inspected them for corrosion, moisture, bent pins and obviously loose wiring and all look good. I cleared the codes and started the rig and had the same code comes back (P0121). I imagine at some point I'm going to have to have the PCM checked. I have also heard ideas referencing the clockspring and battery? As I understand a PCM failure is rare and my battery is only four months old. What other failures could occur to reference the TPS code? Any other ideas are appreciated! Thanks again.
 

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I don't know how you can probe the center pin of the TPS without damaging the weatherseal... but if you can, you should see the voltage to ground there run from about 0.5V to 4.5V as you open the throttle with ignition on.
 

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Either you have a bad TPS, bad connection, wire short or bad ECM.
I'd double check the TPS and wire connection as tomk suggests.

P0121 code.
Possible causes

•Faulty throttle position sensor
•Throttle position sensor harness is open or shorted
•Throttle position sensor circuit poor electrical connection
•Faulty Engine Control Module (ECM)

What does this mean?

When is the code detected?

Malfunction is detected when an excessively low or high voltage from the sensor is sent to ECM.

Possible symptoms

•Engine Light ON (or Service Engine Soon Warning Light)

P0121 Description


The throttle position sensor (TPS) responds to the accelerator pedal movement. This sensor is a kind of potentiometer which transforms the throttle position into output voltage, and emits the voltage signal to the Engine Control Module (ECM). In addition, the sensor detects the opening and closing speed of the throttle valve and feeds the voltage signal to the ECM.

Idle position of the throttle valve is determined by the ECM receiving the signal from the throttle position sensor. This sensor controls engine operation such as fuel cut. On the other hand, the Wide open and closed throttle position switch, which is built into the throttle position sensor unit, is not used for engine control.
 

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As an update: After looking for any other obvious problems I disconnected the battery to clear the codes and kind of forgot about it for about an hour. Hooked the battery back up and the rig still ran rough but no codes until the next day when I got a P0300 code (random misfires). The P0121 still hasn't returned so I'm going down a different rabbit hole for the P0300 and seeing what makes a difference there.
 
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