3hrtour

Hello, Have this 95 e320 cab with 95 k on it. the idle seems to be surging alittle and it runs alttle rough at idle... only at idle. I took it in to the local older benz experts where they did a vacuum test and checked the codes... nothing came up. not sure what else they did but thats all they said. so i picked it up and brought it home. I thought i would put this out on the forum and see what u guys have to say.... next stop will be the dealer. :{

• replaced the engine wiring harness already
• head gasket
• water pump

3hrtour

when all we hear is crickets you know there is a issue. i have done additional home work on this and nothing. its been awhile for the plugs and wires so i am going to replace them as part of on going maintenance..and then off to the dealer

joedb

When you say surge, are you describing an up and down spike in the idle ranginging from 500 to 100 rpm? My 94 e320 is doing the same thing. Sometimes. Usually when it is cold. It seems to do fine when it reaches operating temp. Also I am getting a belt squeal when it is happening during take off. Narrowed that down to a/c belt. Not sure what the problem is though.

uvr708

For me, it was the Mass Air Flow sensor.

Plutoe

How did you make that determination???

uvr708

The car was throwing out a Check Engine light and the code it was indicating was improper voltage to the Mass Air Flow Sensor. The first thing I did was to clean the MAF with MAF cleaner, but that didn't work, so it was clear I needed an entirely new part. And, indeed, I did. It now idles perfectly.

I found this video very helpful for diagnosing the issue:

Plutoe

Thank you----the key words are---"code it was indicating was improper voltage to the Mass Air Flow Sensor"

And the other key element is -----diagnostics

uvr708

Oh and here's one more surefire way to know if it's the MAF -- while it's idling roughly, unplug the connector and see if that clears it up. I did that and the idle smoothed out immediately, so I knew the code it was generating was correct.

fredtga

MAF could be the cause indeed, but first make sure you don't have any vacuum leaks.

pbuchmueller64

MAF get voltage from OVP relay . I had a same problem, same code ( 4) replaced the OVP relay - now OK