Vauxhall Zafira lacking power hesitation

hi my zafira has power loss since i bought it starting to get a bir worse ive googled to see what it could be as its due a m o t and will prob fail on admitions with it and wonderd if any one could help i youtubed it and could be egr valve so i took cover off and egr valve was just under it held on with 2 screws when i took it out there was carbon on it so i cleaned it and it pushes in and out can feel air from it when i pushed it in so put it back on still the same do i need to check and pipes or could it be another problem i watched it on youtube and it said that was egr valve but was easy to get to or have i clean wrong part if any one could help on this would be good thanks