Surging Idle

1991 GS stock with idle that goes up and down about two hundred rpm between 1100 and 1300 rpm. I think this is a idle motor control problem but the ecu gives me a # 13 error - air temp sensor. Bench tested the sensor for resistance and it checks ok. Maybe two problems. Any clues?
Doug

You have idle surge, its really common in 1g's. Check vfaq.com, or dsmtuners.com, or dsmtalk.com. Search for idle surge and you will find more information than you could possibly imagine.

Hope that helps