If your tps was never removed then its more then likely bad. Once they are adjusted once they dont go out of adjustment.
It does sound like a bad tps to me. There is 2 main parts which can cause the timing to jump around. 1 the tps and other is the MAF. More then likely your tps is bad.
Follow the testing procedure from the site I linked you. It will tell you if your tps is bad or not.
If do adjust it, its easier to do it with the throttle body off the engine.
