No kick-down

[cheffy]

My E280 CDi sometimes wont kick-down, its only happened 3 times now, and on 2 occasions, when, say joining a dual carriageway. and I put my foot down, the car judders quite a bit !
On the occasions when it wont kick down, it'll still build up speed, but not very quickly.
I had the ATF changed a couple of months ago (at considerable cost !)
Whats the problem ?

 

[AMGeed]

Could be the throttle position sensor.
It needs Star to diagnose the issue and hopefully there will be some stored fault codes to pinpoint the problem.