98 C230 Transmission kickback & engine rattle
 

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.

Hi,

I am guessing you have 2 seperate problems. Those trans can be finnicky, I have been lucky so far. You can search on "C230 transmission" and probably find quite a bit of info. As for your rattle problem, I had a very similar problem and no one else really did. It sounded to me like knocking and occurred under load as you say, which would be typical of knocking. However, no matter what gas I used it made no difference, whether regular or super duper. I had both a "primary" rattle and also a "parasitic" rattle in the cat which had a loose element on one side. You can test for that by tapping on the cats lightly with a rubber mallet.

I even tested the knock sensor which was fine. I called the dealer and they said I should run REGULAR gas in it. Yeah that's what they said. God only knows why that should make it rattle less!! Anyway one day (after a couple of years) I noticed that I didn't seem to hear it. So sadly I cannot tell you how I "fixed" it. However, changing the cat did make it a lot quieter.

Mike