Volvo V70 2005 The engine works fine until I accelerate then the engine service comes on and engine goes into slow mode until stopped and engine restarted
This is the typical symptom of the exhaust gas recirculation valve failure.
On some vehicles, hard acceleration (or an incline) puts it in limp mode until the engine is restarted.
The valve gets clogged up with carbon deposits over time, which will prevent it from operating properly. Clogged EGR valves can sometimes be cleaned, but replacement is necessary if the valve is faulty, and is much easier.
Here is a related post on a Volvo Owners Club Forum.