Code 121 OBD on 3.9L

1999 1500 van shows 121 error code. Is this hard to fix or simply replacing the throttle position switch? Where is the switch located?

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it is located on the end of the intake on a part called the throttle body
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Now, I am confused! The Haynes manual on Dodge vans says it's a voltage mismatch from the MAP sensor though the obd tester manual said throttle position switch.
truckdriver wrote:

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