So, to summarize, the internal pressure dips below 40 bar and the pump fails to prime with the engine idling, causing the car to go into pressure recovery and it jumps to N.
I understand that they have tried a different TCU in your car but have they attempted to move the bad TCU out of your car and into another to replicate the problem in another vehicle? I'd prefer using the same vehicle from which you removed the TCU the first time.
Has anything on the driver door, window switch, etc., been disconnected or worked on by any chance?
I'm not saying there is no problem with the TCU - I'm just trying to isolate the source before you start throwing money at the car. Although rare, it is possible that the actual coding that controls the pump cycling at idle became corrupt, leaving everything else intact. It is still not a hardware problem, but fixing it won't be easy even at most dealers, if this is the case. All the code is available though MODIS using the SD3, but from what I understand, you need to recognize the missing or corrupt code and that can get complicated.
Erik Di Somma
1989 228 (past)
1985 Quattroporte III (past)