mgzs 2.0l revs to high

Hello iv got a 2.0 turbo petrol engine in my zs I only got it back on the road last night so it was the first time I drove it but the problem is the revs are sticking its not the throttle as thats ok its loose and the cable is ok not to short not to long just right its ok if u drive slow under 50mph but anything over 50mph then the revs stick at 6000 and dont drop any ideas thank you for your help

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