HI guys,

The lamp for "Fault in engine electronic" system has turned ON during the weekend.
I went to mechanic and they decoded the computer the said that it look like either spark plug are duffed or Oxy sensors.
I have replaced the spark plugs and they have tunned the engine (they told me that the engine was "running lean") - set the dwell angle and etc. I have noticed the idle speed is about 920rpm but very stable now is 900rpm but the pin goes up and down just a little bit - I just need to now what is the is that the correct idle speed and should the pin stays stable
And also what exactly could cause oxy sensor failure

Thanks
Kamen

You need a better mechanic. Seriously. Modern engines cannot have the timing altered. Period.
If you had a misfire, you will have gotten 2 codes, one for the misfire and another one for potental damage to the converter or O2 sensor. This is common when the spark plugs need to be replaced.
I hope they cleared the codes leading to the check engine light and all is well now.

Klaus
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Please answer, we need to know if the advice is good or bad. The 164 has a new home, all I am left with are 2 turbos :)

At least on Volvos (and all or nearly all other brands) sold in the US, the fuel mixture, idle speed, dwell angle and related items are not adjustable. There is no "tuneup" procedure or other normal operating adjustments on the engine. Oxygen sensors usually trigger specifically informative codes. Are you sure you are dealing with a competent and honest shop?