I am a fairly new MB owner: 1988 300 SEL. My CEL came on recently, and the car has had a rough idle at start and stops. I took it in to the shop and they told me that I needed a new air mass meter. It seemed like a simple enough job so I ordered the part. Then my cruise control began to fail. It doesn't turn on at all now. After some research it looks as if my problem might be one of three things:
1. throttle actuator
2. air mass meter and separate cruise control issue or
3. some sort of vaccum leak.

It seems that the only way to figure out whether one of the first two is bad is to change it out. But the vacuum lines I can check first, I just don't know how. I have some experience with cars ie: change out the occasional carb, or water pump, but nothing too dramatic.
My question is: how do I check vaccum lines? Which ones would be important to check in this instance?

And do I need to see if I can cancel that air mass meter order and start with the actuator? Thanks for your help.
eric zacharias

1988 300 SEL
1964 Ford Falcon
1994 Isuzu Rodeo

You can use a propper vacume tester, this evacuates the line/s and will show you via the gague if the line is / is not holding vacume.

They are obtainable @ most auto access shops.

Or wet your finger, disconnect both ends, sealing one with de finger and suck on the other end. Block with de tounge and you will feel it either hold onto the tounge...or leak. Cant guarentee the taste though.

Carefull replacing the air/mass flow meter unessesarly. they not cheap.

I've got a W124 300e with a 103 motor, same or simmilar cruie control issues.

Just had the volage regulator changed(it houses the alernator's brushes), and now due to wear, over 230K Kms, have just had the alternator o/hauled.

This is supposed to fix 99% of the problem, re cruise control n/w or intermittent... but alas seems I'm not that lucky.. Battery is new and of correct size.

So the autoelec has just inspected and resoldered all the cruise CU (control unit) incase of poor contacts etc, but he found nothing burnrt out, the pc board was fine and guess what?? It still doesn't work/may work when it feels like it???

The CU is located behind the drivers side kick-panel, incase you need to acess it & do the same.

Suggest you try and follow what I've done so far, it wont cost much and you probaly find your alternator/electrical system needs a breathe of fresh air/repairs.

Best to check one issue @ a time and start @ the begining and work allong those lines I've mentioned. DONT just change the Air Flow, there is also a Zenit type 12v Bosch relay, which controls ALL the voltages. If this plays up, like mine did, it will appear as an inoperative A/F meter or sensor.... so beware he who changes part without correctly testing them 1'st !!!!!!!!!

C how you go & keep us up to date
chow,
Graham

Where is the Zenit type 12v Bosch relay located? I'm beginning to see that there are quite a few problems that can masquerade as air mass meter malfunctions. How did you figure out that the problem was the relay? Did you just have to replace it to see if it was the cause or is there another was to figure out if the relay is bad?