why is mt car using oil on 2008 Volkswagen Passat

My car is using oil and there are no signs of external leaks. The dealer replaced the egr valve but it didn't fix the problem. In 4 months it had almost no oil in it. What is causing this? When you have the car running and remove the dip stick or oil cap, it idles rough. Is that normal?

Asked by for the 2008 Volkswagen Passat
first, you need to check your oil on a regular basis.
when the oil cap is removed while running, it will run rough.
i would have a wet and dry compression test done to check the rings.
have the turbo checked as it can be a cause of oil usage.