accelerator problem

[stevie c1104]

ML 270 02 reg. automatic
when i first get in, in the morning, when the engine is cold the kickdown on the accelerator works fine.
after maybe 5 miles then it stops.
all i get is the normal pick-up instead of instant acceleration.
sometimes during normal pick-up i can get the kickdown no probs.
any ideas please ???
is it a garage job or can i d.i.y..????

 

[dieselman]

EGR valve not opening or closing properly. After xx number of cycles the ECU adopts Limp Home mode so drops the turbo.

Clean the valve and feed pipe out and check the operating vacuum element is working.