Rover 45 facelift weak performance

First of all my english is not so good, please be tolerant.

Its about my R45 2005, 1,6 petrol.

Idle aparently good from outside, but I feel small interference combinated with poor performance. She jump like a "kangoorou" when I decelerate , it feels in gearstick to

Code p0300, not on t4.

Until now:

New fuel and air filters.

New complete ignition.

Catalytic converter looks ok.

No air leak found.

No check engine light.

Sensors cleaned* ( map, iacv, ckp, cam).

Cambelt replaced.

At cold it works better. If she sleep more in the parking (1-2-3 days) its a pleasure to drive...for 15-20 minutes.

Any sugestion?

Thank you !

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