R107 revs oscillate when no throttle...

[ToddGibbs123]

Hi Guys,

Hope you can help with suggestions.

1981 500SL R107. 81k miles, great car

When driving along steady, if I take my foot completely off the throttle but leave it in D the revs drop back to nearly tick-over as expected but then oscillate about +/-300rpm. They do this for a bit, maybe 10 times and then settle. If I do the same but slip it into Neutral the revs drop but just go to a steady tick-over rpm.

Any idea what could be causing this?

Thanks in advance!
Todd.

 

[LostKiwi]

Could be several things.
Idle speed control sticking, bad torque converter, EGR (if fitted) or a vacuum leak.
There's a hard plastic pipe runs from the airbox down behind the power steering pump that can fail.
It probably only does it on overrun because the engine is going excessively lean with increased vacuum.

 

[DREAMER NO2]

Vacuum leak some place . And may be the small micro switch on the throttle cable faulty easy to check just press it with you finger you will hear it click .

 

[ToddGibbs123]

thanks guys - will investigate when I get a moment !

Todd,.