I have two problems with my 1998 C230 sedan with 55K miles on it. Problem 1 - Recently the car has been giving a hard lurch (as if someone rear-ends the vehicle) everytime I come to a quick stop. It's as if the transmission is slamming when downshifting to it's last gear before stopping. The problem is less obvious if I brake slowly and come to a slow rolling stop.

Problem 2 - My "engine valves" rattles very heavily when the car reaches normally operating temperature or after the car has been idling for a long period. The rattling is especially pronounced if I leave the automatic transmission in "W" mode whilst driving. The rattling is coming from the left front underhood area. Surprisingly the noise only occurs when the car is actually driving and I'm accelerating putting a load on the engine. If I keep the car in neutral/park and rev the engine there is very little rattling. Or if I accelerate slowing the rattling isn't as heavy.

So far I've taken the car to two separate shops and they've changed spark plugs (twice); replaced air mass meter (twice); replaced front oxygen sensor; changed transmission fluid (twice; temporarily fixing the transmission lurching problem for about a month); removed and serviced the cooling fan, and did several unscheduled oil change replacing the engine oil with castrol full synthetic 10W 30W.

Does anyone have any suggestion on sorting these problems? Is the transmission lurching and valve rattling problem related or are they separate issue. At this point I'm clueless and I think my mechanics are also.