I would welcome thoughts about where to look to cure the hesitation and stalling that has started to occur after some emissions system work. Here's the saga:

(1) Needed headlight replaced. Shop installed new ballast while headlights were on. Gave car back with giant red battery lit on dashboard.

(2) Diagnosis: Need new alternator. Swore it was just a coincidence. Installed new alternator, but techs were banging around in there trying to get old one out. Waited for guy who works on MB often, who just disconnected some wires and hoses and did the replacement zip zip. New alternator solved the problem and works well. However, gave car back with Check Engine light on.

(3) I assumed Check Engine would disappear, but it didn't. Shop pulled codes, and said they normally indicated need new EGR valve and new MAP sensor, but first try 4-step engine cleaning and replace air filters, which were plainly dirty. They did that, cleared codes, and Check Engine came back on within 5 miles. Car ran better than ever and idled smoother than ever, however, so the cleaning wasn't a total waste.

(4) To clear check engine lights, shop replaced MAP Sensor and EGR with BWD/Intermotor parts. Check engine light cleared, but immediately noticed hesitation when accelerating from low RPM situations, like when you come up to a red light and it turns green just as you are coming to a stop. Also, when you accelerate hard, there doesn't seem to be quite as much power as before, as if it's summer and the a/c is on. Oddly, transmission seems to shift much more smoothly than before through all throttle ranges (it makes sense that it could operate differently as it is controlled by the computer). The problematic hesitation has now turned to almost-stalls, including one frightening one last night where the car stalled as I tried to accelerate after slowing for a light, all the dash lights came on, the steering wheel locked up, I was thrown forward and then the engine caught and restarted as I was trying to hit the brake.

(5) The shop said there were no codes present when I brought the car in before the problem last night, and they can't diagnose the problem without codes.

Obviously, I need a new shop, but if something jumps out to you all about something that may have been not properly installed or disconnected while doing the tasks above, please let me know. They claim that if the parts were bad, or the vacuum was off-spec, we would get a Check Engine light. I'm happy to swap the parts for the Bosch OEM MAP sensor and the Piersburg OEM EGR valve, as they are essentially the same price as the BWD, but I'm thinking that it was likely the work that was done rather than the parts that is the problem.

I would be eternally-grateful for your thoughts, as I would prefer not to have to go to the Stealer.

 

Does the shop have Mercedes equipment to get the codes or is it a generic system? You need a shop that can do star diagnostic.

 

Just generic code reader. I was actually thinking of getting my own Star Diagnostic, as the prices have really gone through the floor, but just finding a good shop that isn't the dealer would be better. Still looking...

 

My car kept stalling due to a defective crankshaft position sensor.
The engine would shut down whenever the car was moving at low speeds or when it came to a stop.
I replaced it last Friday, by myself, and the problem went away.
Currently, working on replacing the boot on one of the cv joints.