C30 Engine : C30 2.0L loosing power when warm

[rules]

Hi All

My C30 seems to run fine until it gets to normal operating temperature and then it seems to loose power. It still feels "fine" until about 2500-3000rpm and then it has this weird hesitation (like you can put your foot flat on the accelerator and barely anything happens) and to make it weird it sort of comes right higher up the rev range (can't recall how high up, possibly around 4500). So it doesn't loose power completely it just sort of levels off.

Some years back I had a similar issue with a V70 and it ended up being an ignition coil so I've replaced them all so far but no luck. To make it even trickier, it doesn't always happen.

I've asked the independent dealer to have a look last time it was serviced but they said all was fine so I assume there were no codes.

Any ideas?

Thanks,
R