I have a 1994 Mustang GT 5.0 5-speed and I replaced the idle air control valve and I've cleaned the throttle body and still getting a surging idle What could it be??? Plz help
It's not a bad surging idol but it does die sometimes when you stop It surges from about 600 RPMs to about 1,200 RPMs
There are a few things that could be the cause:
1. Clogged fuel filter: Check to make sure the filter is flowing well.
2. Clogged fuel injector: If you haven't done so recently, run some fuel injector cleaner through it. See if that helps.
3. Vaccum Leak: Check your hoses and anything rubber/plastic for any holes, cracks, or signs of wear.
4. Fuel Pump: Pressure test the fuel pump to make sure you are getting enough fuel through the lines.
Those are how I would start, in order. 
Could it be the throttle position sensor???
It could be but it sounds like a fuel related issue.