Alfanuts

New R500 owner herewith a huge mystery that no mechanic has been able to diagnose 100 percent yet. As noted in title, when accelerating weather forma stand still or passing someone one freeway, you get a havey pronounced shuddrr that feels its coming frm the back of the car. If i step on the gas heavily you dont feel anything. Its only when you modeatly accelerate. Happens every time cold or warm engineor temperaure doesnt make any difference. Als it makes nomdifference of its in C or S mode.

Proble number 2 is whenturning wheels all the way waether roght or left and at low speedsor from sanding still the car will roll a couple of feet byitself without hitting the gas ( as normal ) but then will come to a complete stop as if i just hit the brakes to stip it and will not move unless i hit the gas really hard to move it and you can feel it fighting you back as if the brakes are applied.

Any ideas?? I read jus aboutevrything online regarding the aove two issues but there is nothing that duplicaes exactly what im experiencing.

I got several mechaics (mercedes and others) give me diagnosis from steering rack to differential to esp to transmission to angle sensors to speed sensors. Im ging insane trying to figure it out. I dnt want to take it to mercedes dealer as i do not trust them.

The car is a R500 wth regular struts and 117k miles. The steering does moan when turning btw. Tranny shifts very smooth all the time. Theonly true diagnostic i got is one high end shop hooked up their computer to it and told me its 100 percent the steering rack causing all this mayhem as thats the code they got from scanning the computer. Is that possible?

Any input will be grealy appreciated.