High Idle with Check Engine Light

[fly1747]

1996 Outback Wagon with 2.2L engine. Car has recently suffered from
an occasional high idle, above 1000 rpm and higher when the A/C
compressor kicks on. Today it was idling normally and then started
idling high and the check engine light came on.

Any ideas before I go and have the code read?

Also, the gas cap was not fully tightened when I checked it this
morning.

Thanks,
Matt

 

[.._..]

Try starting it cold. Is the warm up idle the same speed as the abnormal
idle?

I might suspect a bad thermometer (car thinks it's cold when it is warm
causing the "warm up" sequence to continue).