surge on decel?
 

Hello all,
It's been a while since I've posted. I'm just back from yet another trip to the desert. Glad to be back. Things are insane over there, worse than what CNN shows. Hopefully that was my last tour, we'll see.

Anyway, here's my question of the day. My 87 420 is still doing well. I have an issue with a surging during decelaration. It happens when the car downshifts while coasting to a stop. It's very noticeable, I can feel it as well as see it on the tach and oil pressure guage. The tach moves up and down about 1-2 hundred rpm. The oil guage bounces from just above 0 to about 1 bar. Once the car comes to a stop the surge is gone, idle is rock steady at about 700 and oil pressure is a little over 1 bar. Air temps have been around 85 - 90 degrees. The weird part is that if I have the a/c on then there is no surging. Also if I'm in a low speed situation like a parking lot, the car surges constantly below about 10 mph unless I keep my foot lightly on the gas. Otherwise it seems to run just fine. My last tank averaged just over 21 MPG in mixed driving. Any ideas what could be causing the surging?? Thanks guys.

I'm thinking that if you have one, check you throttle microswitch. It's supposed to cut-off the gas when you take your foot off the accelerator.

My 420sel Does That When I Coast. Not Sure Why

I was referring to the to the small switch at the end of the throttle linkage. Normally gray with a small wheel at the end of the actuator. I think user_name is referring to the throttle position switch.