Hello This could be a lack of fuel pressure from the electrical pump at the tank. If the connections to this are corroded or damaged then the pump could stop at any time or could not be running at full speed. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse, Ideally measure the pressure at the inlet to the main engine fuel pump and if this is low check the pump as described and also consider changing the fuel filter as if this partially blocked this too will reduce pressure.
Also the EGR (Exhaust Gas Recirculation) valve could be at fault. This valve pipes some exhaust back into the intake to help clean the emissions up. Generally this reduces performance a little and is usually switched off when the car is accelerating if it’s stuck in position then you'll be pumping in exhaust all the time which won't help the power. Check that the valve connector plug and its wiring is OK and any vacuum rubber lines aren't split or broken. If this is all OK you may want to consider changing the valve