For the last while now the bus finds it difficult start first thing in the morning or when cold , coughing , spluttering and white smoke for about 30 seconds , then all returns to normal .
I've changed the heater plugs and the cold start solenoid but the problem persists , where else do you all recommend I look ?
Would the heater plug relay cause this and how do I check that it still works , I'm a bit of a numpty when it comes to electrics

Any and all advice greatly appreciated
Thanks in advance
Brian