1991 Honda idle RPMs jumps from 1500 to 2000 and back in 1 second intervals on cold start?

My 1991 Honda Accord - When starting cold, the RPMs will jump from 1500 to 2000 back to 1500, and so on back and forth and 1 second intervals until the engine is warmed up and then idles at a constant RPM. What would cause this?|||Your idle speed control motor is malfunctioning at lower temps. Not an easy nor a cheap fix. It has to be replaced.