1989 300E Starting problem

[300ESUPER]

I have posted this problem before and received some great feedback, I also checked the site for people with the same problem.

When I start the car I have to hold the key for a while and step on the gas pedal until the car turns on. When the car finally starts it idels rough for about 15 to 20 seconds then the car is smooth. The car has no problem when driving only when starting. The colder it gets the harder it is to start. I have just changed in the last month:

2 fuel pumps
dist cap and rotor
fuel filter ( 6 months ago)
air filter
water temp sensor

I have changed the spark plugs 8 months ago and the ignition wires 4 years ago. Would these 2 things cause the car not to start properly?

I have run out of ideas!!

Please help

Fab