My 850 turbo (190,000 mi) in the past week has had throttle problems - accelerates to 3500 rpms by itself while driving or other times. Lubed and checked the throttle cable. Its okay and attached to the firewall. I was just sitting in it idling in park and the throttle rev'd up to 3500 rpms without touching the gas pedal.
Punched the pedal - didn't help.
Went out and jiggled the cable - didn't help.
Shifted into gear - didn't help.
Finally shut it off. Now it won't start. It wouldn't start earlier today but started this evening alright, but after this happened it won't start. I presume it won't start because the throttle is wide open.
What's causing this?

 

Did you ever solve this problem? My car is doing the same thing.

 

I had to take it into Volvo. They replaced something with the throttle. Seem to recall it cost me about $700 - not sure.

 

The only electronic part on the throttle body is the TPS-Throttle Position Sensor. It was probably dying or had poor connection. The ECU was receiving incorrect signal from the TPS...just a possibility.


JPN

 

There is also the IAC motor (idle air control). It's not physically part of the throttle body but it would account for an erratic idle and if it stuck open would cause a hard or no start condition. The cost sounds about right for an IAC too.