It is interesting to troubleshoot purely on symptoms, but it is also a bit stumbling in blind. Some measurements as discussed earlier or some faut codes would be helpful.
Last time we cocluded, that the cold start valve was erroneously energized when i shouldn't, from the fact that the car ran fine with the cold start valve disconnected. This is apparently not the whole story.
If it really does some difference to disconnect the cold start valve, it also means that it is actually energizing, where it should not, which leaves the fuel pump relay as prime suspect.
Assuming this is right, we have to look for, what else goes wrong. Bearing in mind that the fuel pump relay contains a logic circuitry to control various things including fuel pump and cold start valve, it is possible that it not only tells the cold start valve to operate incorrectly but also the fuel pump. So, are you sure, that the symptom now (with cold start valve disconnected) is flooding and not starving ?
Anyway, if above is true, it puzzles me that the car still runs with OVP relay disconnected. If cold start valve floods the engine with OVP relay connected (ECU operative), it should also flood it with OVP relay disconnected (ECU inoperative), unless the mixture by coincidence remains within acceptable limits.
So if above track is wrong, my next suspect would be the EHA (electrohydraulic actuator), which is located on the backside of the fuel distributor. This unit adjusts the fuel pressure to the injectors according to the ECU control signals, as previously described (earlier I did not realize, that the fuel pressure regulator, you talked about, was the regulator for the pressure input to the entire injection system).
I recently had a fault in it, which caused flooding always, so the engine wouldn't even start.