noise from metering head

:cry: hi my mk1 golf 1600 when it has warmed up makes a banging noise that come from the metering head it is as if the flap in side is hitting the cage.
can someone help me?

i'm not to "up" on these, but does the car idle ok?
and have you looked inside the airbox?

It idles fine at first and runs fine, its only when you turn it off and back on again does it have a problem. Bad idle and very low on power. Air box is clean.