RPM Surge while coasting

[vrsmith]

When my 560SEL is coasting, especially downhill, there is a very noticeable surging happening. The tachometer shows 200-300 rpm changes but you can feel it as well. Since it happens while coasting, it seems to be related to a sensor reading the high vacuum incorrectly. Could this be a problem with the oxygen sensor or some other sensor?

Thanks,

[mbdoc]

For emission control there is a ""fuel shut-off"" durning decel, sounds like your car is turning this on & off too quickly.

[fredsegal]

How would I adjust the fuel shut off?

[dpetryk]

You dont. The fuel cut off is controlled by the Lambda computer. Both of my 420's do the same thing. Its normal.

[goldenbear]

vrsmith,

Does the engine exhibit the same surging at a standstill idle?

[vrsmith]

I won't say that the idle is perfectly smooth, but it doesn't seem too bad. It is only noticeable on the highway.

[500sec]

My friends 1995 S320 has the same problem.He asks me to fix it every time i drive in the car with him.is it normal

[dpetryk]

Its normal.

[vrsmith]

This behavior can't be normal; at least not to the extent that it happens with my car. When I first got it, it didn't do it at all. Now I feel it is quite prominent. I'm thinking of changing the oxygen sensor first since it is easy to do and likely due since they are rated for 60K or so.

[Benzmac]

My suggestion is to make sure that the throttle "closed switch is working when hot. I have seen them fail in this manner.