Vauxhall Astra where do i find the egr valve under bonnet

I read your previous problem down the list, I'd check the pipe that goes from the front of the car, alongside the battery, to the front of the rocker cover and to the boost solenoid, it's a thin black pipe that gives vaccuum to the boost solenoid, if this becomes kinked on the rocker cover corner, you'll experience lack of power, also if the rubber sleeves that the pipe starts and finishes in are split - this will also affect it.