420 surges while coasting downhill....HELP!
 

Hoping someone can help me with this problem: (1986 420sel)while coasting downhill at any speed I am experiencing a decelerating surge...feels like someone is pressing the brake pedal on and off. One other thing that is occuring that may be related is a decrease in fuel economy....gone from 20 mpg to 13 mpg?

Any ideas...help?

gb*kw

Bribenz - I appreciate your reply. Could you please clarify what are you calling the "eha"...my book doesn't reference it anywhere.

respectfully...gb*kw

Bribenz -

1. Disconnected the eha and surging did not stop. Any other thoughts?

2. Is the throttle position switch replaceable by itself or does the throttle body go with it?

thanks again...gb*kw

Similar problem on my 560SL
 

I have a similar problem on my '86 560SL that is unresolved. I'm thinking a vacuum leak may cause such a problem, but would welcome any other ideas???

Thanks, Ryan

amazing - my 420SEL has exact same symptoms - took it to MB dealer after posting similar thread in shopforum, and they replaced the O2 sensor - which did nothing for the surge (bounces from 1300 up to 1500 when coasting) or fuel economy - so I'm back to square one - there has to be a common answer out there somewhere ....

JoeB

Joe B -

Seems odd that so many people confirm having this same problem, yet no one knows the cure. Mine too oscilates between 1300 & 1500 rpm??

Anyone out there with some input?? So far we got a throttle position switch and an O2 sensor.

gb*kw

gb*kw/JoeB:

Did either of you ever get to the bottom of this? I'm planning on working on it over spring.

Thanks, Ryan