Volvo: 2000 S80 vibration when accellerating over 40mph, oxygen sensors, bulb failure

Question
Clarification: Dealer does not think that problem is with electrical or engine, but front bearings and axle. This is absurd, car sometimes drives OK which is only 5% of times. If the problem was mechanical it would be all the times.

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Followup To
Question -
First it started as throttle body problem, then 2 oxygen sensors were replaced. Still after driving 2 days Emission Light and Check engine light comes on and back to dealer (this is 4th time). Last time we were told that problem is mechanical bearings loose and axial shaft, however when driving on flat surface or down hill there is no vibration.It apears as insufficient power at higher speeds. Spark plugs were replaced, still the same. There is also intermittently light bulb failure showing once in a while.

Please advise what could cause this sluggish performance?

Dealer said that all looks OK, this is the reason he started to look for mechanical problems. This looks like an electrical problem.

Linda
Answer -
I don't know much about the S series, but if the dealer thinks it is electrically based, then I'm suprised his computer diagnostics didn't pick anything up.  My first thought would be a timing issue.  This year car, the computer dynamically controls the timing based on several factors, including the feedback from numerous sensors.  I say timing, because that can cause a lack of power with vibrations, and can also perpetuate as you go to higher and higher speeds (increased RPM's, essentially).  Beyond that generic advice, I don't have any specific remedies, other than to suggest to the dealer to use a computer diagnostic if they haven't already, and to maybe concentrate on the timing control issues that might be causing it, like a crank position sensor, etc.  Good luck!

Answer
I would agree that it seems odd a mechanical problem would only manifest itself part of the time.  On a car this new, a mechanical failure of that nature seems unlikely.  I think my original advice still stands, I would have him do a thorough diagnostic on the computer for timing issues.