Help: 850r with a mind of its own

[jreed]

I wrote up a quick DIY on how I removed, cleaned and reinstalled the IAC valve. This cleaning procedure eliminated the strange surging idle and stalling problems I was experiencing in hot weather this summer after the car was already warmed up.

https://www.matthewsvolvosite.com/forums ... =1&t=47533

[swedishmeatball88]

hey guys. So it can't, or likely isn't the maf because i replaced it with a new one 10 months ago, and i change the filter every time i change the oil, so I doubt that went again.

So everything looked fine and the car was functioning great, except for the CEL or the o2 sensor. Driving home, i was slowing down going around an onramp, going probably 35 miles an hour, when the coolant temp gauge dropped and the car jumped from 1500 rpms to around 2500 and stayed there, and the car was unresponsive to the gas pedal. Pulled the car over and turned it off. Check all the fluids, everything looked fine, so I went to start it again and it wouldn't start, radio came on, but not the engine, I pumped the gas pedal and it came on, but the engine started to accelerate, and was approaching 6000 rpms, so I turned it off. I tried a couple more times and finally got it to start, and drop it for 30 minutes home, without any problems. This was suggested earlier, but is it the transmission? the issue only comes up when I'm slowing down and in the first gear range of speeds.

Thanks for all your help.

[rspi]

The first thing I would do is replace the coolant temp sensor. If the sensor tells the computer it's cold, it may tell the car to idle high because it's cold when it's not.

The idle control value is also a high possibility.

[swedishmeatball88]

i'm going to replace the coolant temp sensor, and can I get a used one from any 850, or does it have to be new?

Also, the turbo doesn't seem to engage any more, if I accelerate hard, the turbo never kicks in.

[pkc303]

I would use a new one. They are not that expensive, and they control a lot of stuff.