PEUGEOT 405 2.0GRi

[cafferkeys]

I have recently re-built the bottom half of this engine and it starts and runs ok. When it is started from cold it fires immediatley and will rev up (if the throttle is pressed on and off) perfectly for about 5-6 seconds. At this point if the throttle is suddenly depressed the engine will hesistate for a second before it actually revs up. This will stay like it even when hot. Also when you are travelling along the road if you put your foot down hard the car accelerates perfect but if you accelerate gently (especially at low revs) the engine judders slightly. The spark plugs are white/grey indicating that the engine is running weak. I have had a diagnostics unit plugged into the ECU which records a "knock sensor signal fault" - i have replaced this sensor and checked the wiring from the sensor to the ECU but still the fault is registered. I have also renewed the inlet manifold gaskets in case there was an air leak there but the problem is still there. Can the ignition timing and mixture be adjusted on these engines??? It has a Magneti Marelli 8P injection system.
Can anybody help???