chucai

I had this idling problem few months back , and since then i have brought my car back to Mercedes dealer 4-5 times. They still havent seem to fix the problem. This unstable idling doesnt always occur, it only does sometimes when i was on "D" with my legs on the brakes the brakes at the lights. The car seemed to be unstable...like going to die. But went i shift the gear to "n" it will be fine again.
Beside that, last yesterday when i accelerate my car above 3000 rpm , i was suprised to feel like it was having a fuel cut ! the car just wont go . Now my car is again in the dealer. They told me i have a faulty valve for the bad idling and very bad air filter for the power cut.
Have you guys encoutered any of these problems..??
By the way, i drive a dec. 2001 c240 (c203)