What are the symptoms of a bad TPS sensor?

How exactly would the car act with a bad TPS, what are the symptoms, and could it possibly cause poor idle?

When mine fried and died, the engine wouldn't even start. If I unplugged it, it would start right up, but while running if I plugged it back in the engine would stall...

hmm...

Well I ask because my engine will start but the rpms will just fall. The last couple of times the engine hasn't even tried to correct itself. I just have to keep my foot on the gas to keep it running, but if i let off the rpms just drop and the engine stalls :S