Well my best guess is that the heads need to be
rebuilt i recently am having the same problem with
the 1998 bmw 740i 4.4l, i smoke tested it and it
does have a intake gasket leak so by sending the
heads off to be rebuilt i will be replacing those as
well, i am a certified tech and i get no codes besides
misfires from the intake leak, nothing for the dohc
sensors. When it does happen in mine i do hear
valve chatter and it even does it after idling for a
while and then taking off. So now i just need to save
up get a side car and begin tearing apart the motor