Car not running boosting correctly
 

Hi guy have a couple problems with my car been trying to sort them before asking on hear so far changed coil pack plug leads bov gasket all vac/boost lines cleaned icv cleaned maf and had it on my scanner codes are nock sensor and maf and 02 sensor but maf and 02 are not together when I scan it one time it will say maf I'll clear it next time it will say 02 sensor . Basically its started idling funny it will be idling fine and then just suddenly drop rpm then pick back up but it's only slightly but I can feel it misfiring like running lumpy though the car next problem is when driving it it's not spoiling getting to full boost as quick as it was I was getting full boost between 2500 and 3000 rpm and holding it steady now It ain't boosting untill 3000 to 4000 rpm also when in boost it dont feel like its boosting properly not pulling me back in my seat like it was feels like its hesitating when on boost am I right in thinking it needs the nock sensor changing as its pulling timing out causing this shuld mention i have done boost leak test aswell and found nothing recently fitted a car back exhaust and forge bov but car was running sweet after I fitted them up untill today .also have a vibrating coming from front under my pedals felt mainly though the accelerator pedal this happens around same time this boost problem did any help be much appreciated cars a UK turbo 2000

A faulty maf will give a lack of boost or too much sometimes, plus poor idling , it won’t show as a cel as it’s not something that shows a cel if it’s at fault , an 02 sensor that’s faulty is likely to just over fuel the car , is fuel pump pressure ok on and off boost ? you can buy a simple gauge plumb it into the fuel line to test it , take off fuel pressure regulator air pipe and you will get off and on boost pressure , if the pressure needle is jumping all over the place or pressure is low then fuel pump issue , i’m assuming plugs and leads etc are ok , don’t know if that helps ?

Is it a MY99/00 uk2000?
You've fitted a decat system? That won't help
Is it a vta Bov? Won't help either.
Any other mods?
Guessing you're running standard tune?

I'd check the up pipe and it's gaskets for leaks