Power loss

Good to all.
First of all, thank the possible answers.
I am a mechanic fans, but there are things that escape me.
I tell you my problem:
I have a C 1.7 dt Corsa, well, working in perfection, until one day you notice a loss of power in the middle of the highway, swim of black or white smoke or blue, no witness in the painting, oil level well.
Nor say that when I get to a slope, it runs out of force.
I have changed the air filter recently.
There are times that the power enters and sometimes not.
Could it be the EGR valve, some type of turbo sleeve?
Thanks and a hug

It is possible that it is the egr or some sleeve as you say .... I think it is the egr ... if it were a sleeve would pour a lot of black smoke ... especially in the accelerations.