Volvo 1800ES engine oscillating

Hello everyone.
I am facing a strange problem on a Volvo 1800ES.

I deeply revised this engine : every injection component is matching with the car, temperature sensors resistance are ok (cold and warm), TPS is brand new and MPS sensor has been rebuilt by Bosch (Nuremberg). O-rings between injectors housings and cylinder head are new (it's a common way of false air). The car has run perfectly for a couple of weeks, then suddently had a problem : cold idle speed has dropped to 500 rpm and when engine is warming up, engine speed starts to oscillate.

I checked today :
- MPS internal resistances --> ok
- TPS adjustment --> ok
- engine air flap --> ok
- additional air for cold idle os closed when engine is hot --> ok
- ignition coil internal resistances --> ok on low and high voltage sides
- spark plugs are normal and well tightened
- no fuel leak
- fuel pressure is 2.1 bar
- injectors are clicking normally when engine flap opens --> injectors are working
- hose between intake manifold and MPS sensor is ok (no crack, collars are thightened)

Here is a video of the engine behavior (warm engine) : 

I read here in the past that sometimes D-Jetronic engines can oscillate, but I can't find the source anymore.
Any help is welcome ! Thank you !
 

Hi Pierre,

what I write now is only possible if u have 0280000009 or 0280000017 ECU. Those have overrun shutoff. in idle. Remove TPS connector and try again. If you have high rpm but no heavy oscillating ( we call it sawing)  then you have massive false air. RPM goes up, ECU shuts off, RPM falls down, ECU starts to inject again, ...

Thank you very much, I'll try as soon as possible and keep you informed.