Spluttering/black smoke when driving in traffic

I've a similar problem with the kangoo as some otehrs here-when driving in traffic (stop/start etc) or having made a journey and then hopped out of car (engine cooling for e.g. 15mins) I get lots of spluttering and lots of smoke..i know black smoke indicates fuel problems anyway but im sort of stumped..filters/air ok..not burning oil..is there a way of testing if it's the injectors or a solenoid valve or something?..ive a feeling its a problem with the amount of fuel being delivered to injectors (but van runs fine when on open road..anyway it makes driving in a city almost impossible..help appreciated greatly!