I have a 2000 f150 v8 4.6 sometimes while at a light the rpms drop then surges. Rpm go up then drop to normal. I was thinking maybe throttle position sensor. I've changed the transmission fluid and filter and cleaned throttle body out of all the carbon. And k&n filter system cleaned out also. Any suggestions what to do next.

 

sounds like a vacuum leak. Broken hose or intake gasket leak could be letting extra air in causing the rpm surge. Listen for a whistle. If there isnt one take some water/soap and put it in a spray bottle and with the engine running spray vacuum connections and any gasket that connects to the intake and watch the bubbles to see if they get sucked in. Do things one by one to elimanate them.