1991 Volkswagen Jetta RPM's surging at idle

I have a 91 vw jetta gli 16v. I have a problem with it that I think may be electrical. It doesnt always happen but ussaully does it the most after restarting the car. While driving when I let off the throttle to shift the rpms surge up to around about an extra 1000 rpms and come back down to around 1500 rpms. On a good day ill idle nicely at 1000 rpm. But when it comes down it will continue to reff repeatedly until I come to a complete stop.I thought it was the throttle position sensor and replaced it. That did nothing. Im not sure what it could be. But any help would be greatly appreicated. Thank you