It's a 2000 car, and it should go like the clappers. However, it doesn't. It's hard to put into words the exact malaise, but I'll have a go:

When started cold, it's almost lumpy, and extra unresponsive. When it's warmed up, putting your foot down results in a noticeable lag (can be a couple of seconds), then usually it gets moving and changes down.

Putting your foot down "properly" i.e. slamming it down and activating the kickdown switch usually results in a lag during which nothing much happens, then a massive jerk as it suddenly changes down and gets going. Most of the time, a second after that, it loses most of its power, the ESP and BAS lights come on, and the car seems to be in some sort of limp-home mode, you certainly can't drive it properly. Switching the ignition off and then the engine back on clears the fault and one may proceed on one's way.

It's recently been serviced, and the mechanic said there was a fault code for a misfire, but he couldn't work out why, so he reset it and said see how it goes. Well, it's crap again, and I'm not about to give the car back to him.

I had an idea that it might be the MAF, but I'm not about to go replacing expensive parts on a whim, plus does the MAF not raise a fault code when it's broken? Someone else suggested a blocked exhaust / cat, but again it's just guessing.

Anyone got any ideas about getting to the root of the problem?

 

I had a similar experience. Look for my posts on it. You might have the same root cause...

I tried the MAF fist but that did not fix it. The next move was the Throttle Position Sensor, which is at the end onf the throttle cable near the drivers side firewall. That did the trick. You can get them from Autohaus in AZ.

 

Well, there's no TPS code being thrown as far as I know. I had a look at your thread and it does sound vaguely similar, especially the delayed shove in the back when accelerating. Did you ever kickdown hard and find it wouldn't change up a gear, just sat there revving at the top of the rev range?

Was it an easy part to replace? Do you remember the Mercedes part number?

 

The code I had was a P0120, if I recall, and that points to the TPS. Also there is a post somewhere that lists all the MB codes, so go somewhere and see of you have any stored. It's all in that old thread if you can find it.

I did not have kick-down troubles per-se, just a slow-motion throttle response, or no response at all.

If you call Autohaus they can get you the OEM parts without the MB Dealer markups. They are the sames parts, just with different part numbers.

Replacing the parts like the MAF and TPS are simple, just be carefule and take your time. The hardest part for me was getting the airbox seated correctly. You might want to see if yours is on the correctly first. An air leak where it meets the MAF can cause all kinds of strange things.