E320 1996 Light throttle surge
 

After fixing various other issues with my E320 - I have one last minor niggle.

When applying light throttle, around 1100 rpm - the revs will surge up and down about 400 rpm. This only happens when hot. Say about 85 C engine temp.

Also when hot, coasting down hill sees a small pulse of about 200 rpm also around the same RPM.

Every other aspect about running the car is perfect. No Codes.

Other things replaced include:

CPS and K40 - to fix a hot stalling issue and a non restart till cold.
MAF - Rough running and surging at idle issues.
Wiring harness is perfect - have cut back and inspected wires.
Head Gasket done - EGR vaccum hoses were reversed by mechanic - have just verified this. Also tested EGR - applying vaccum makes car stumble at idle.
Cleaned throttle body.

I suspected it could be a sticking EGR valve (the one on top of the manifold).

The fuel system shuts off injectors during coasting to reduce emissions & that can cause the surge. So that is normal.

Surge
 

I'm resurecting this as the symptoms have got worse. Tends to be reversing. The revs will drop then rev up once you take your foot off the accelerator.

When driving around parking lots, at about 20kph the car pulses.

I had a hunch so i disconnected the power to the purge valve and plugged the vaccuum line. The pulse is gone, idle is very rough like this.

I have also cleaned the egr and it is fine.