Misfiring and backfire, codes P0300 and P310B

I have a the vehicle listed above fsi
.
It has been misfiring at random. The PCV pipe was broken and replaced it but it keeps misfiring. I replaced the spark plugs, petrol filter and coil packs and still misfiring. It just flashes the check light after 10 seconds when I start it always and worse when its in neutral or slowing down approaching traffic lights or stop sign. Now there is a pop sound at the exhaust especially when I take off my foot off the gas pedal when reducing speed or just after revving. The pop is like an explosion sound like, I am not sure if the catalytic converter was removed or its there and it has a booster in the exhaust. When its idling especially at a stop sign the idle will be rough but when the check light begins to flash the idle improves there. When I start in the morning when it is a bit cold it may stall but when I start second time pressing gas pedal it will then start rough.
It is throwing these DTCs P1403 EGR System: Regulation Deviation
P0300 random misfiring for cylinder 1 2 and 3.
P310B fuel Pressure regulation. What could be the cause of this endless misfiring.