Sharpen
Last night I ran your' problem by a Cappuccino expert. He was broadly in agreement with all that Midship has said.
Substitution of parts is a good method of fault finding. I am fortunate with my son also owning a Beat, but it is the only other one I have ever seen!
My Cappuccino mate added, check battery condition. and try injector cleaner. If the injectors were gumming up this would have the greatest effect at idle. The latter point is still following Midships thinking.
Good luck
Jerry.