E240 unusual vibration

I have a 1999 E240 Auto (W210 I believe) and I suspect a slight but perhaps worsening vibration problems. Symptoms are not confined to the same area:
(a) I was always amazed at the smoothness when stationary at engine idle even in "Drive" but now occasionally I have been aware of slight vibration felt through the steering wheel. If I move to "Neutral" the vibration ceases. In a MB web forum I read about "balancer" replacement but have never seen this discussed in this group. Could this be the cause?
The other problem...
(b) At speed of around 80 mph there is a pronounced vibration felt more generally than through the steering wheel. It is just like a out of balance wheel but my wheels have been balanced. Again I have read that this 1999 E240 vehicle has this characteristic. Is this fact?
MB service record is complete and no problems reported by or as yet to MB.
Beemer
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Beemer,
I don't believe that the harmonic crankshaft balancer (aka "the hand grenade option") would cause this sort of vibration. Usually there is a slight knocking sound before they shatter. Now of you haven't had yours replaced in 60K miles then it's time to have it done anyway.
How many miles are on the car? If it's in tune, then perhaps your engine mounts are worn (they're fluid-filled and when they leak you might see some oil-like residue on a cross-beam just behind the engine). I can't speak for a 240 vibration at 80mph, but the 320's I have don't do this. I seem to recall that tires out of balance usually cause a vibration at more like 50-60mph, but then again most tire shops don't do that good a job at balancing tires for higher speeds and if you have old/cheap rubber then this could be the culprit. Other than that, your front-end might need some care and attention - perhaps the steering dampener is shot or a wheel bearing is gone.
Josh

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Josh,
Thanks for the advice. I'm beginning to think it is the tyres even although they were synamically balanced. They will be due for replacement soon so this will help identify the problem.
Beemer

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The idle vibration could be from a marginal spark plug, a marginal ignition wire, dirty fuel injector, etc etc. Adding a can of fuel injector cleaner to the fuel is a painless start and eliminates the fuel injector possibility. After that it's $$.
Tires have a static and a dynamic balance, at 80 mph the dynamic balance is the issue. Have a different tire shop check the tires for dynamic (high speed) balance.
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Yes but the idle vibration is only when moved from Neutral the Drive
Beemer
The idle vibration could be from a marginal spark plug, a marginal ignition wire, dirty fuel injector, etc etc. Adding a can of fuel injector cleaner to the fuel is a painless start and eliminates the fuel injector possibility. After that it's $$.
Tires have a static and a dynamic balance, at 80 mph the dynamic balance is the issue. Have a different tire shop check the tires for dynamic (high speed) balance.
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