VOLKSWAGEN GOLF ENGINE POOR MILEAGE

My Car Is Heavy On Petrol It Takes Out Black Smoke And Pinks It Switches Off Almost Every Stop. Please Help Me Cannot Even Drive The Car As...

I Get About 36 Mpg On Motorway And It Is A 2l Diesel And About 18-20 Mpg In City. But The Car Does Not Feel Like It Is Drinking A Lot Of...