Strange TPS behaviour

Hello everyone,

I am facing a strange behaviour on a Volvo 1800ES MY72.

Preliminary checks show that every and each part of D-Jet injection is the right one (correct Bosch ID).

The car has some hesitations at low speed / low load. It starts fine and runs quite well. CO is around 2.3% at idle.

Pressure sensor was not holding vacuum (from -0,4 bar to almost 0 in 20 seconds), I changed it for a good (electrical and pneumatical) one.

In order to find the culprit of those hesitations, I tested the TPS, at first on the engine with ignition ON and fuel pump fuse removed. 

Here is a video of the test (please raise up the sound level in order to hear the clicks) : 

The problem is that the injectors are triggered either on acceleration and deceleration, although the internal switch that cuts the circuit for deceleration works well. I cleaned the TPS tracks gently with electrical contact cleaner, with no success (same behaviour).

Wires on the car harness correspond exactly to the numbers engraved on the TPS, so the TPS is correctly wired.

To confirm this problem I removed the TPS from the engine and tested it on the table.

Here is the video link :

This time, pulses are only generated when turning the axis CCW, means acceleration. When turning it CW (deceleration) no pulse is generated.
Close examination of the TPS contacts and other elements did not show any failure 

I removed the ECU to check any strange thing around it but everything is clear and clean (at least outside and around the connector).

The question is : what makes the TPS do different things when on the table and on the engine ? As it is directly wired to the ECU, I would incriminate the ECU.

Any suggestion or correction would be greatly appreciated !