Why is my Mercedes 190 e 2.6 hard to start while cold only?

depending on year..... (fuel injection)cold start valve not working try removing it and clean it with carb cleaner if it dont work replace it. (carburettor when cold only) choke not working undo the 3 small screws holdong the choke mechanism to the carb turn the choke unit so the tension on the brass butterfly tightens (at top of carb primary venturi) but not too much if the butterfly is already shut speed up the choke idle speed located behind and to the rear of the choke mechanism. damp in ignition system ( but this would usuall cause running problems too) remove distributor cap dry inside with a rag and spray wd40 or water repellant and refit cap.. also spray around spark plugs and coil, but remember to dry first cos wd4o can trap the damp inside added by bheilers: you also might consider checking the OVPR (overvoltage Protection Relay) located on the firewall in the engine compartment behind the batter on most models. It would either have 2 10 amp fuses on the top or if its a aftermarket brand, would have a single 10amp fuse. Check the fuse(s) if they or it is blown replace and try starting the car again. the OVPR is a common issue with the 190 and 300 series MB's