High idle on defrost

This is Kevin with NWA Auto Shop. Without seeing the vehicle, I can only theorize. Based on the limited information given, these are my thoughts. A) Some Defrosters use the A/C to remove the humidity in the air (newer models), A/C bumps up the idle. B) A vacuum leak can cause a higher idle. Some Climate controls use vacuum to operate. C) A PCV Valve or Throttle Position Sensor may be faulty. As this is a 97 with OBDII I would scan (more than global, manufacturer specific) the vehicle for DTC's (diagnostic trouble codes) and Live Data stream to see what is happening in real time. Hope this helps.