Ruaway Volvo- Intermittent Fast Idle
 

Does anyone have any ideas-

I was on vacation for about two weeks. When I got home my 96 850 started right upp and off I went. About a mile from home I noticed when I let off the gas it was still accelerating with the RPM not dropping below 1700. When I thought it may be unsafe I put it in neutral and stopped the car. The RPM went to about three so I shut it off to not hurt anything. Then I tried to start it with no success three or four times. I wated a few minutes and it fired right up. It has happened about three times in the past few days, but I have been letting it rev up since it holds no higer than 2000 rpm and eventually it will just go back to normal while I am driving. Any ideas before I take it to the shop?

RE: Ruaway Volvo- Intermittent Fast Idle
 

I experienced similar symptoms with my 850 Turbo. I had it towed to the shop and they said it was the Coolant Temperature Sensor. They replaced it and the car was fixed. Maybe.. just maybe.. yours is also the coolant temperature sensor. (But I have no idea why this sensor failing would cause the car to rev like it did.)

Good luck!

RE: Ruaway Volvo- Intermittent Fast Idle
 

I would also clean the idle motor it might be jamming.

RE: Ruaway Volvo- Intermittent Fast Idle
 

Also see if you can pull codes via OBD-II at a local AutoZone; they provide free diagnostic service. If there is no AZ near you, other parts shops may provide the same service.

http://www.autozone.com/store_locator/home.htm

The coolant temp sensor sends signal to the ECU and the ECU adjusts the idle RPM. When the coolant is cold, the engine requires more fuel to sustain idle with thick oil (oil gets thicker & more viscous when cold). This makes the engine to idle at faster RPM but it should settle down to 850 RPM or so after the coolant warms up. The sensor is nothing but a thermistor; a device that changes electrical resistance (Ω) according to the coolant temperature.


JPN