W203 C240 2.6 Loss of power beyond 3000rpm

[urbanjoggergb]

my 2001 C240 manual has developed a fault where it losses power/runs rough after 3000 rpm when under normal load. I have checked for error codes and none have been logged, I have replaced the fuel filter and an independent garage has confirmed the bosch air mass sensor is working fine.
Any ideas where I go next?... Thanks

 

[DSM10000]

Was the diagnosis made using a Mercedes Star computer? Generic OBD readers are very limited. Find a local MB specialist.