MERCEDES BENZ E220 N REG - problem with car starting in direct sunlight - stones

Can anyone help, I have a mercedes benz e220 n reg, if I leave it in direct sunlight or heat it struggles to start but when it is not sunny or a hot day it starts straight away, could this be a faulty automatic choke, overnight it starts fine would be grateful of your help

MERCEDES BENZ E220 N REG - problem with car starting in direct sunlight - Peter.N.

Does the starter turn over at normal speed when it won't start?

MERCEDES BENZ E220 N REG - problem with car starting in direct sunlight - galileo

Any possibility this is a vapour lock problem - petrol evaporating in the fuel system when hot?