CLK 230 Kompressor running lumpy- HELP!

[Charlie Beech]

When I'm tootling along at a steady 20-25 mph it feels like someone is pulling the handbrake on and off (slightly). On hard acceleration the speed increases in stages and doesn't feel smooth until beyond 4,000 rpm. When changing down (say 4th to 3rd) at speed, the car has a sort of lag, a bit like the handbrake syndrome again. I've taken the car to three garages (two with diagnostic facilities) and none of them can find anything wrong with it (although one of them admits it's not running properly but doesn't know what it is). Please can somebody help me!!?? I'm close to taking a sledgehammer to the damn thing and buying a Jap car instead.

 

[jberks]

Charlie,
To be fair, it could be anything from ignition to ECU to fuel supply. I know exactly how you feel. I had a lumpy running problem that the garages inc the dealer told me didn't exist as the diagnostic showed no faults. I was close to selling the car. As a last stab, I managed to demonstrate the fault to my local specialist to the point where they agreed it wasn't right.
I chose a specialist as
a) they are a hell of a lot cheaper on labour (and it may take a while)
b) they know a lot more about mercs than the dealer
c) As they see older ones, they are more likely to have seen the fault before.
d) They can swap parts off other cars and try them. - If they dont work you just pay for the time.
e) they have ethics so you're not likely to pay for all the time taken.

I then handed them the keys and explained that I didn't want it back until it was right - however long it took (and by the way, I was keeping their loan car!)
4 days later and a lovely sweet V6 was returned to me.
Good luck,
JB