that is right what Mbshop sayed.If you sayed about the tune up was done 2,500 km ago,but what was done at the time?i see you do not drive the car a lot .So first i would do a proper tune up.Plugs air filter (if clean leave it)fuel filter ,and check cap and rotors.And it might be good also to check the resistance of the spark plug cables .Have you checked if the eha is leaking?But usally at that milage what is going on is that the fuel injectors are leaking.When you shut of the car the extra fuel goes into the cylinders and gives to much fuel at once at start up.But if you replkace the injectors do not get the brass once.There spray pattern is verrrrry bad and half of them are screwed ,make sure you use the steel once,awailable from MB.Also a goog idea is to bleed the fuel distibutor when you replaced the injectors or fuel filter.
There is more ,but these are the first things you shoud do or look for.
Another thing i might mention ,but a loooot of the other members dont see it my may,is to rerplace your timing chain and tensioner.So there is another forum in here that everyone disagreas with ne,but they are not the onse repairing the cars afterward ,which is me,they are the one paying the 2g for the jobthese are my my advises and stick to it...Harald