WBX running weak

[Budgie7]

Hi , my van a 2.1 dj auto and whilst checking the emissions found it to be running very week. Any ideas as to why or what causes this .It was reading 0.5 and adjusted it and is now about 1.8 on the mot gas analyser
Thanks for any help

[kevtherev]

Vacuum leaks can create a lean-running engine that requires extra fuel to balance the fuel mixture. condition is more likely a fuel delivery problem (weak fuel pump, restricted fuel filter, dirty fuel injectors or a leaky fuel pressure regulator) than a vacuum leak.