The car starts as it should every morning. I drive 30 minutes to work with no issues.
After sitting a couple hours, I restart it. Idle goes to 1500.....when I put it in drive or back in park, it starts to surge between about 700 to 1500. The engine check light comes on for about 30 seconds then off.
The car will continue to surge until warm and idle is below 1000, then it runs as it should.
I get a code 15 (coolant sensor circuit).
Question: How would the coolant sensor be related to the surging?
From searches: I thought it may be the IAC or EGR.......
I have 165k and have never cleaned/changed the IAC or EGR....
Any help would be greatly appreciated.
Note: I checked the coolant sensor wires......do I need to check connection at the ECM?

 

might be unrelated.. surging could be caused by a vaccum leak.. any whistling sounds? have you check your vac lines? thats my best guess.. maybe someone else has a better idea