Passat 2002 TDI does'nt start in the morning
 

I have Passat 2002, 1,9 tdi 96kw.

Couple of months ago I drove accidentally my fuel tank almost empty (car was parked on the slope that moment and forepart was above). After that car doesn't start normally in the morning anymore. It sputter once and then need to be kick-start 2-3 minutes. After that it starts arduously and with tremble. If it starts, there is absolutely no problem to start it even 10 times successively and it starting easily all day.
Strange thing is that if I park on the slope and car forepart is below, car starts with no problems in the morning also.

Engine works normally, fuel consumption is same and I haven't noticed any loss of power. Maybe engine vibrates a bit more than earlier, but it is'nt much more.

Diagnostics doesn't show any errors. Fuel filter (together with valve on it) is changed. All glow plugs and gaskets below fuel injectors is changed as well. But it still doesn't start normally in the morning. I don't know what to do and unfortunately my mechanic either. Also I still have no clue, is this problem connected with empting fuel tank or not.

I would be very thankful, if somebody can give any advice or information.