Suzuki Vitara engine dies occasionly wont tick over

I have this annoying fault, been suffering it for years and it is getting more frequent.
When it is running fine the tick over is sweet as a nut, about 500 to 600 revs. I can drive like this for weeks, then out of the blue I will be driving it and come to a stop,say give way,and she will die on me, as if I turned off the ignition although all the relavent lights will be on I can start it up and then have to keep the throttle up to stop stalling, this can happen in cold, dry,freezing any season. I have looked at other forums and have a suspicion on the potentiometer that is in the throttle positioning sensor,I also have jumped out and turned several times the throttle linkage to see if this works and sometimes the car resorts back to tick over. Lastly how do I get the right part, what info do I need and where to get parts, thanks in advance everyone