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Q: p1120 out of service code

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I have been having issues with my car engine somtimes racing by it self and then settling down to normal.I had the throttle body replaced on the recommendation of a yourmechanic now the car is not shifting properly it somtimes will not shift out of first or second gear and the check engine light came on.the car ran fine for one day after he installed the new throttle body which actually is a used throttle body because they do not make throttle bodys for my car any more.It did it today on the way home it woul not shift out of second but after I drove the car for a while it was running normallyI took it to advance auto and got a scan.P1120 out of service.Can you help me.I can give more details if need be.
My car has 188000 miles.
My car has an automatic transmission.

Hi. The code P1120 is a problem with the throttle position sensor. The input from the throttle position was not what the computer expected and would cause the computer to go into a failure limp mode. When the computer is in this mode, you will have low power and transmission shifting will be harsh and erratic. This is normal for the computer, as it limits some operations during a major throttle position failure. You will have to replace the throttle sensor with a new one to ensure this problem is resolved. Used parts cannot be guaranteed to work, but if the part is no longer available through the dealer or aftermarket, then a used one is the only way to go. It is hit or miss on used parts. If you need further assistance, I recommend you have a certified technician, like one from YourMechanic, replace the throttle position sensor and inspect for other possible failing components on your vehicle.

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