when taking the car out of gear, or slowing down for traffic lights, my idle is all over the place, and actually cut out once....can anyone diagnose the problem, i've been told it could be one of three things, either needs a good service (happening tomorrow), the airflow meter or lack of performance air filter. car has full decat system to get rid of gases, but nothing to suck in. oh and also its running rich on fuel, so been told it could need mapping. any of these a possibility? i'm not mechanically minded so have no idea. any input will be greatly recieved.

 

Could be the MAF, just disconnect it with the engine running. If it stalls it is working, if it still runs then the ECU as taken over the fueling. This is not 100%, but, its a very good indication. When servicing prefill the oil filter before fitting, this will avoid any oil starvation on start up. Good luck.