if u clean your boost hoses off from the top of intercooler to charge carrier .....over time if not cleaned it gets full of oil ...this is from the turbo....it gets through the seal and builds up in your pipes...so wehn u dump your getting the smell from inside coming out and then through your heater system. if its excessive oil build then i recommend a turbo service kit..around £70...happened to me and i just cleaned and put back together no smell

ps: if its not that then its possible its overfueling....rich mix?