Hi all,
Need a little help here. My 850 seems to wants to rev up on its own. I was at a red light and heard the car rev and shake a bit. When the light turned green, I let off the brake and the car wanted to go with no gas on. I drove home and put it in park. I sat for a bit with no gas or brake on and then the rpms started going up to around 2500-3000 then back to 1000. Like I was reving the engine but not touching anything. It did it a few times then I shut her off.

Any thoughts or ideas would be greatly appreciated.

Bad idle air controller?

Thanks, you nailed it. Temp sensor was also faulty. Changed both and my baby is running great now.

MAF comes to mind. A 'normal' air leak would not cause the idle to go up/down. So the ECU/ECM is changing the mixture.
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My back feels better when I sit in a Volvo seat

I had a rev problem with a 960 Volvo when cold only and the problem was fixed by replacing the temperature sensor!

Thanks for the input. Temp sensor was faulty as well as the idle air controller. Both were replaced and the car is running great now. Seems to get better mileage too.

my '97 855 did the same thing. It was the cruise control computer and i unplugged it. No problems since.....

Thanks for the reply.
Since it's a quick replacement job, I swapped the MAF sensor with a used one from a parts car I have. The problem is still there. I wonder if both parts are bad. Do you know if the MAF is a part on the 850 T5R's that's known for going bad?

FWIW, I had 2 new in a sealed box Bosch MAF sensors that were bad.
Both failed within 3,000 miles.
Purchased from a reputable parts house (that took both back for full refund).

I suspect there was a run of faulty MAF sensors a few years ago.
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"Differences of opinions should be tolerated, but not if they're too different' - Sharon Craig

I can't imagine they would both be bad.