Check your fuel pressure.
For background.
The fuel pump delivers a certain pressure, let's say 3.5 bar. The injection system needs 3 bar (I'm not sure exactly what pressure is needed on the LQ9 engines). That's why you have a pressure regulator on the engine, on your fuel rail, that releases the excess pressure and directs that fuel back to your tank. It sits on the driver side of your engine.
This is necessary because your engine control implements the calculated injection quantity based on the opening times of the injection valve.
If the fuel pressure is wrong, the injection quantity is wrong, your engine is not running proper.
At the front of the injection rail is a valve where you can attach a manometer to measure the pressure.
This is the injector rail. On the right side of the picture is the front of your engine. You are practically looking at the fuel rail from the passenger side. In the background you can see the two connections for the fuel lines, supply and return, and the integrated pressure regulator. On the bracket that takes the pressure to the other side of the engine, you will see a plastic cap where the valve is to measure the pressure.
If the pressure isn't right, there's something wrong with the pump, the fuel filter is clogged, a line is pinched, or whatever.