Peugeot boxer without power, does not accelerate well

I'd really appreciate your help with a problem. I have a 2003 Boxer 2.0 HDI. I had a starting problem, caused by excessive fuel return from an injector. I repaired it, but now it doesn't have the same power. It takes a long time to accelerate on straightaways or hills, and it quickly loses power. Other symptoms I've noticed include excessive fuel consumption, a lot of smoke in second gear, and the lights are constantly flickering, as if the voltage is fluctuating, but I checked it and it's steady. Someone suggested the EGR valve might have a lot of soot buildup.

What else could be wrong?

I hope you can help me.

The EGR valve is the main cause of these problems in Peugeots; you should clean it. It's a factor that causes this symptom, not the only one, but it's what usually fails. Try cleaning it and let me know how it goes.

Thank you for the quick response, but could you tell me the proper technique for cleaning or washing this EGR valve?
I hope you can guide me.