Hey guys just wondering if anyone could help me with my boost problem, 

So I boost up to 1 bar of boost , if I hold it at 1 bar of boost for one second my car will start judder and struggle for power  then my boost just dies down, when that happens my engine management light starts flashing saying there's a misfire.

 

I've replaced the map sensor and the maf sensor but no luck .

Have you considered actually reading the fault codes rather than just throwing money at the problem?

Yes I've read the codes and nothing seems to show up apart from cylinder misfire 

 

Well, there are other things that cause misfires too. Does your code have a cylinder number associated with it, because I can think of at least 2 things that cause a misfire on one cylinder and not the other 3 (coil pack and spark plug).

It does say cylinder 2 misfire but that only shows when I take it to top boost and boost cuts out , I remember when I first mapped it , it was at 1.5 bar but only 1 bar now , could this be because of faulty coil pack , That's why it's not going to 1.5 bar  

 

Well, in an extreme case a misfire could be a "not fire", which reduces the volume of gas generated per unit time by a quarter. This could be a coil pack or a bad plug.

Alright cool I'll check it out 

I vote coil packs.

Just a quick thought as your car is mapped, what brand and grade of plugs are you running, and moreso, what gap are they set to?. Most mapped cars tend to run NGK BKR7E plugs gapped at 0.7mm.

 

If the answers to the above question are satisfactory, then its another vote for coil packs or the wiring to that pack, as the insulation can harden and crack shorting out in the damp.