Hi, im new here and I have some questions about my moms 1994 C220. Im home for the summer so she wants me to fix it up because she hardly drives it anymore. She's had it for a while now, she bought it from the dealer here preowned back in 1998 I think. Recently she's been having some wierd problems with it..

The first problem was if she used the horn it would blow the A/C fuse, we replaced the horns so thats stopped.. Now here are the real problems.. Around the same time we noticed that we'd hear the door lock system going for at least 5-10 minutes after we got into the car or locked it.. Now, the doors wont lock so she has to lock them all individually and she also has to lock the trunk.. You dont hear the lock system humming anymore.. Also, at the same time the A/C is acting wierd... If you turn it on it will blow air (it is cooling fine so it seems) through the side vents but nothing comes out of the center vents on the dash.. Sometimes it will, I guess due to the climate control system or something but i'd say most of the time nothing comes out of those 2 vents.

While I was at the dealer getting the horns I asked the guy about the door lock problems and he said it could be some vaccuum pump leak or something in the car but then after he did some double checking he said that there is no pump in our car (1994 C220) and that he has no clue what it could be (he wanted to see the car but the car isnt in the US and I was in Atlanta at the time).

The last problem is the car seems to be idling strangely, like its floating or something.. When we intially start the car we have to give it some gas so it'll start up and once we let go of the gas the idle speed will drop below 500rpm, this is when it feels like its gonna shut off, then quickly(I mean really abruptly) speed up to about 700/800rpm.. This floating idle thing also happens when we're at lights or at a complete stop.. When we're coming to a stop and braking it feels like it wants to shutoff, the car jerks a bit then the speed quickly jumps up and idles at the correct speed.. Sometimes it does shutoff when we brake hard like a sudden stop or a quick takeoff or something like that.. Could this be the Mass Airflow Sensor/Meter or is there something else that could be causing the problem? I think this car did this in the past and the dealer told her it was the throttle and replaced that for her but I dont remember the problem ever being completely resolved because most of the time we've had this car we've had to give it gas to get it started.

I searched the forums around here as well as some other sites and people mention this pump so my question is, does this car have this vaccuum door lock system that I see talk about around here or does it use some other system? Could the door lock problem and the A/C problem be related to the same issue?

PS: The check engine light or whatever mercedes calls it is on and has been on for some time now by the way.

Thanks in advance and any help would be greatly appreciated!