re92

Hi,

First post and new to the world of Mercedes.
The car in question is a 2005 W203 C180 Kompressor with Automatic Transmission and 80k miles on the clock.

Car idles fine when in P but as soon as it is shifted into R or D it starts to judder. The revs drop and the car struggles to keep a stable idle, feels like the throttle is oscillating.
The problem got a little more severe this morning on cold start where it flagged up a red "Battery Alternator Visit workshop" error on the dash.

I've only had the car for two weeks and the idle has been slightly uneven but not problematic. When I purchased the car the seller told me he had recently replaced the alternator.
After some forum searching most threads point towards the voltage regulator being at fault here but since the alternator was replaced recently it should be new. I need to get under the bonnet and check exactly what parts are new and what brand.

Also one thread mentioned to check the pulleys that drive the alternator to make sure they aren't slipping.

Does anyone have any diagnostic advice here that I can add to the above list? I'll be getting the spanners out on the weekend so I can add any suggestions onto the work list.

wlsorensen

My C230 M271 engine did the same exact thing. It ended up being the VR. I had a Valeo Alternator which have known issues with VR going bad. I even put in a new rebuilt Alternator and it did the same thing, just at a different point during warm up. I finally just replaced the VR for $40 after reading about the hidden voltage reading on my W203 model. I could see the voltage moving from 14.1 to 12.5 and all over the place. With the new VR, 14.2 with a low of 13.7. It runs like a new machine. In the M271 engine, you can also put in a Bosch, it is interchangeable and I would do that if I had it to do over again. The connector is identical. they used two vendors for the alternators for the 2004 M271 engine. Most re-manufactures DON'T replace the VR unless it tests bad. In my case the issue fluctuates but in making the decision to just do the VR this lats time around, in removing it off the rebuilt it was clearly the OEM and had not been replaced. So having dealt with all Valeo rebuilds, it is clear that the issue with bad VRs is not being caught during the testing. Just get a Bosch if you have that option.