Renault Scenic engine cuts out when i start the engine if i don't rev. the engine sometimes

I have had exactly the same problem as you. The problem escalates as well. Mine was slow to start and then after driving for two minutes and slowing down the engine died. It became more and more frequent and like you I had to rev the engine and keep a high RPM to make it go. Eventually the engine cut out in high speed.

I was first told the throttle had to be cleaned out and after a "quick" clean by RAC it got ten times worse. VW cleaned it properly out and said nothing was wrong with my car but on collecting it it failed for them too. They have now changed the air mass meter £210 and I could drive it home today without a single problem. The car feels better than when I bought it 6 years ago. It seems like a problem that is not easy to discover and goes unseen when the diagnose it by use of computers. I am no car expert but I think you may have to change the air mass meter as I did. Best of luck!

You may like to have a look at the pipe which brings the air in from the atmosphere. You may find a kind of bottle. if the connection is not air tight the result can be that which you are experiencing. This doesn't cost hundreds and is proven to be a solution.