1998 Mercedes A160 semi Automatic

Mercedes » A-Class » 1997-2004
Question

Hi all,recently purchased A160 for daughter and all was good when I got it but now throwing up fault code P1504 on my MBll scanner,when I try to clear code it clears but comes straight back,also hear single click from engine bay once code comes back??
I was thinking of getting MAF air mass meter repaired,will this fix problem???
Any help would be greatly appreciated ?
Jimarco71