Cleaned the throttle body and changed the gasket, but it seems it doesn't help.no errors found too

Hello everyone..my s80 is acting strange sometimes.Usually on cold starts car idles ~1500rmp for a 15-20sec then drops off to the 1000 and when warms it goes to 750 or so.. But sometimes from a cold start the car idles at 1200rmp 2-3 seconds and then drops to 1000. It happened 3 or 4 times during th...