Also, try a software update for Engine ECU / BSI and Gearbox ECU. Also, after update you will probably see that all the injectors are fine with no need to change. +1 for the coolant temp sensor as stated above by @Paul H. BTW you don`t have an throtle body like petrol engines. You have an air distributor. Usualy no carbon is build there but you can check it anyway. Also, check that your turbo deliver the desired pressure - requested by engine ECU at low RPM (until 2100 rpm) you may have some problems there too.