My car is an automatic which shudders slightlt whem i pull away , and also when driving the engine seams to rev slightly but not on tick over , pls help thanks

which engine, what year.?
egr struck open , partially is #1 cause of low idle
and never getting a tuneup.

the ECU, does all it can to hold 800, hot, all day,no matter what.
but
will fail if:
1: not tuned up, called misfire. (shudders is misfire)
2: too lean (low fuel pressure.)
3: leaking injectors, more misfire. (or clogged)
4: egr stuck open a tad, or stalls if open fully.
5: ISC stuck closed.

That is when clutch slip happens-when the clutch is released. If the clutch disc is worn badly, it won't hold tight against the engine flywheel-it will slip, causing that shudder you feel. Have a mechanic verify this, but it sounds like you need a new clutch.

Bad spark plug or wire. Observe it while running at night to see if spark is jumping.

Adrian, try changing the fuel filter first and see if that does anything.
OR you might have got some bad gas somewhere with some water in it. Get some "Dry gas" at an auto parts store and add a couple bottles to the gas tank. I'd try this before you bring it to a mechanic.

Sounds like the gearbox filter need replacing,,, very common... drain oil . remove gearbox sump. filter right there,

http://dieselgiant.com/mercedestransmissionfluidchange.htm

check teh engine breather pipes ,they could be cracked or split sucking in air

Yep , you will have to get the engine light code cleared at a garage , or buy the relevant OBD Code reader from E-BAY . They are fairly priced .

if it is under warranty the dealer should have no choice, but you can check this out just in case.
http://www.lemonlawamerica.com/

difficult one this without haveing a drive in car to hear the noise,this sort of sound could be caused by the flex plate on the crank/torque converter,break on edge of fan belt,power steering pump,altenator bearing,evan the transmission possibly a pump,or could it sound more a sort of electro mechanical noise ?? without hearing it its very difficult to diagnose .

Yes. Sounds like a plugged Trans filter or burned fluid. A full service on the Trans usually runs about $90 and is money well spent.

Another problem-which bugged me for 3 months, and had your similar symptoms, was a worn out fan clutch. It sent a shudder throughout the vehicle which mimicked a transmission issue. I know it sounds silly, but a new fan clutch cured my shifting issues.

The fan should rotate smoothly with some resistance (Engine OFF, of course) If you feel binding of any kinf, it probably is bad. Also check to see if you can cause movement fore and aft. If you can get it to rock back and forth, it is bad and needs to be replaced.

A fan clutch for that vehicle usually runs about $55