This morning traveling to work, leaving the town all was normal, drove 10kms to the first village & under the street lights I could see clouds of white smoke behind the car. I immediately checked temp, pulled in & stopped the engine. The smoke immediately stopped so it was coming from the exhaust & not something else burning. The smoke had a toxic / acidic smell & definitely not oil or fuel smell. I found nothing wrong, then restarted the engine & all was well again, running perfect & not a trace of any smoke. The car is a V6 E320cdi fitted with a DPF. Is this smoke a normal process of a DPF cleaning process, as I can’t find any other reason for the smoke. Any advice or ideas would be appreciated.