Just in the past few weeks my 1993 850 has started idling erratically at start up. At the same time it started idling erratically on bumps. However, generally once it warms up it idles very smooth. I cleaned the battery terminals, the idle air control valve,the flame trap and the throttle body. I also put a can of BG fuel injector cleaner in. Didn't help.

The diagnostic unit showed a bad signal from the throttle position sensor. I cleared it, same problem but no new fault code. Obviously, I suspect that the throttle position sensor is going out. I had similar symptoms 6 years ago and fixed it this way, at the time the car was 6 years old, so maybe I am due. This time though, the car is acting a little different, because last time under pressure the engine surged.

So hear is the question, has anyone ever actually fixed an idle issue by changing the O2 sensor? If so what was the car doing? Is there any maintenance that can be done to an O2 sensor, ie clean it, grease it.

Thanks,

Hi:

I read in Haynes manaul that the fuel vapor charcoal canister can cause erratic idle when it goes bad too. It's under the drivers front fender.

Check your MAF too...maybe clean it (don't touch it...just spray contact cleaner on it and let it dry).
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1998 S70 T5 Emarald Green Metallic (125K), 2004 V70 2.5T Ruby Red (45K), Previous Owner of Black '94 850 Turbo Wagon (Sold at 140K and miss her). My cars have been running so well lately they've got me worried.

Have you checked your vacuum lines? They have a tendancy to break and get brittle too. They will also set off your lamda light and 02 sensor errors and cause uneven idle surging.