my audi 80 is misfiring after engine start
 

what can i do and what is the causes

There are many things that could cause this. You would want to start with checking/replacing spark plugs and wires, while you are there putting in a new distributor cap and rotor would be a good idea. But that is just step one and may not fix it. Fuel could be an issue, try a new filter these are the relatively cheap/easy things that could be done in less than a couple hours.