I have a 2002 Mk 1 Octavia VRS standard and have owned it from new. Recently I am experiencing a power dip on acceleration, I have also just changed air filter. No fault codes any idea,s

Have you fitted an oiled filter?,is so you may have contaminated the MAF with oil

No, I fitted a skoda origional all done very cleanly. Problem only really noticable on hard acceration when lifting foot off the throttle dip is there on 1 in 5 bursts, could this be an overactive dump valve?

Probably the N75 valve, I had similar, fitted a new one and it's a lot smoother

I think it was the N75 valve, problem has solved itself . I think because I must have been driving with a ****ty air filter (probably due to driving in Spain) the N75 valve was only opening 75% and maybe produced a grease ring inside the solenoid valve at the 75% mark and when the car could breath again the N75 opened 100% and stuck for a second and kept the waste gate open causing the dip. A week of acceleration bursts has cleared the problem. Thanks for the help.