Hi I'm Jacob and I need help!!!

I have a 2003 Honda Accord EX, 2.4L. I keep getting a check engine light for Throttle Position Sensor (TPS codes P0122 & P1121). Also the car keeps jumping, it dips down real low in RPMs for a few seconds and then gains it back. It does this every minute or so. I have 5 volts coming in to the TPS but don't have any volts reading at the signal out lead. I have replaced the TPS twice and it hasn't fixed the problem. If I unplug the harness from the TPS sensor and run a test wire from the 5 volts harness wire to prong on TPS and the negative to its prong I get 4.5 volts coming out of sensor and 5 volts when I accelerate indicating that the TPS is working, but as soon as I plug the harness back into the sensor I loose all volts coming out of sensor. I've also tested connectivity for the signal out line from the plug to the end of harness and I have no brakes in the line. Can someone else tell me what's wrong or what to test next?