Does the engine malfunction light come on when you get the power loss? Often when this happens with this engine, It will give fault codes for throttle body and throttle position sensor but, It will be the ECU at fault.

A terribly bad design to bolt a computer to the end of a cylinder head where it is subject to huge thermal cycling. They later realised the erro of their ways and put the ECU in the wheel arch where it is subject to water and dirt instead!

In 99% of the cases of this problem with these it will be the ECU at fault and will give fault codes for various other things.

Forget using Vauxhall dealers as they will charge more than the car is worth. You can use an independant or buy a used ECU kit from a salvage yard and change all the relative parts so you won't need to have it reprogrammed to your car.

This is one of the many reasons, I'd not buy a Vauxhall - poor design.

You'll need the ECU, Transponder ring from around the ignition barrel and the chip from inside the key.

Change all 3 and it will save you having to have it programmed but, Make sure it is from the same spec car as you have.

Might be worth getting diagnostic check done first just to make sure.