why does my car accelerate and decelerate, and stall when stopped?? on 1995 Nissan 200SX

I have owned this car for 4 years, and it has been a nice reliable vehicle. Until recently the cars rpms have been fluctuating up and down, sometimes up to 2200 rpms, and sometimes so low that it stalls, why??

Asked by for the 1995 Nissan 200SX
It could be many things, unfortunately and without experiencing the problem first hand or being able to do some basic diagnostic tests its hard to say. It could be an idle control motor issue, low coolant level could cause this as well, or possibly a vacuum leak could cause an erratic idle.