please Help fault codes!...running rough

[Melvi]

good evening!

car been running like "poo" recently, so I plugged a cheap code reader in and got:

00561 - Mixture Adaptation

16514 - Oxygen (Lambda) Sensor

I have a 1.8T AGU, with eBay job De-Cat on, and a K and N air filter.

when idling it feels like its misfiring, and when in 4/5 gear it judders and has loss of power, and sometimes feels like a lot of lag in turbo compared to normal - this however has only happened a couple times though.

the second code has been there since fitting the De-cat, so am i right in thinking thats the issue?
and the the other code i noticed today.

kinda a noob with these engines, so any help much appreciated?

[stfc_gti]

00561 - Mixture Adaptation

 00561 - Mixture Adaptation: Adaptation Limit (Add) Exceeded

 Possible Symptoms
 Engine Jolting
 Increased Fuel Consumption
 Poor Idling/Jolting
 Reduced Boost Pressure

 Possible Causes
 Mass Air Flow Sensor (G70) faulty
 Fuel Pressure too Low
 Leaks in Intake Air System and/or Exhaust System
 Injector(s) faulty (i.e. coked)

 Possible Solutions
 Refuel Vehicle
 Check Fuel System Pressure
 Check Mass Air Flow Sensor (G70)
 Check Intake Air System and Exhaust System for Leaks
 Check Injection Quantity
 Check Injector(s)

[GTi_James]

MAF, coilpacks, full service, PVC system conversion, blowing exhaust, oxygen sensor, temp sensor, clean your injectors and plugs, run redex fuel system clean...(the red bottle for petrol) 

[Mr_Orange]

.......running like "poo" ...........

........16514 - Oxygen (Lambda) Sensor............

...........eBay job De-Cat on...........

[Melvi]

cheers for replies!

will check all the above at weekend, with regards to checking the MAF, is there anything specific to look for that might me a clue if its this thats causing the fault?

also how to test the fuel pressure?

going to the lambda sensor, am pretty certain its due to my De-cat, due to MOT next month the Cat will be going back on, so suppose will see if the code comes back then. unless there are any other ways of telling if the lambda sensor has gone?

cheers and sorry if these are stuid Q's... 

[GTi_James]

maf off and run for a few minutes, dont know about fuel pressure myself and putting the OEM cat back on will most probably sort out the lambda, give it a clean as well