Grande Punto Help!

[Matgreg47]

Hi guys , I'm new to the site and need some help with a turbo stutter issue on my grande tjet. When I come to the turbo rev range to engage the turbo the car sort of stutters a bit the engages but it feels like I'm not getting the full power from the turbo. Any ideas???? Please help. I recently changed the oil type to 0w40??