I bought my forth Durango the other day as I've sold all my others and missed them I decided to buy one as a fixer upper and this one runs rough has a code for tps po121 I believe so I checked it out today and it's idling real rough doesn't have much power when driving exhaust is shaky and the motor makes a ping noise sounds like coming from under th Intake. This is a 4.7 automatic btw. Has 185k miles and is very clean. I changed the spark plugs to the dealer recommended and made sure they were gapped right I check for voltage to all the coils and all the same at 14v with it running I back probed each one. Then I replaced the tps with one from oreillys seems to run a bit better but not much and still get the code after resetting it several times. I also cleaned the throttle body and the iac witch didn't seem to bad. Not super dirty voltage on battery is good amperage for alternator in spec. So I tested the tps I'm getting five volts to it with it in the on position. Then when open throttle and back probing it to test voltage it goes up to about 3.7 volts wide open. Not sure if that's in spec or not but even at idle it's running rough. I haven't had any other codes for crankshaft or iac or camshaft sensor or anything I don't want to just start throwing parts at it. Also after replacing the tps it's idling at about 1000 rpms witch is high however no more pinging sound coming from the intake area. I'm stumped at this point any advice much appreciated. I'm a full time student at a local auto tech program however my teachers havnt had any advice other than check the rocker arms. And my teacher who's the electrical genius is out of town or something. Please help

 

A general measurement is: at idle = .5 Volts; full throttle = 4.5 Volts. If the PCM detects that the throttle angle is greater or less than it should be for a specific RPM, it will set this code.

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thought id share!