when i turn car off then restart the car the problem is gone for a short period of time but later returns. I also noticed that a flap inside the tail pipe on drivers side is closed preventing fumes from escaping. when this flap is open the car seems to be ok. I have read a lot about emission problems online but nothing about this flap inside of tail pipe. I don't know how this exhaust systom operates or if this flap even has anything to do with problem I am having.