Hi, I have 2001 DeVille and I have a overwhelming exhaust fumes coming from my under my hood. it seems to be coming from the passenger side of the engine. at the moment I have no check engine light on. but I know something isn't right. it can run ruff sometimes when starting it. but not always and it doesn't stall out nor does it idle ruff when at a stop light. I wish I could tell you more than that but that's all I know. I was hoping some of you could give me some ideas on whats happing and possible ideas of how to resolve this issue. thanks for any and all help. oh I have noticed a decrease in gas mileage from 12mpg to know 9mpg since this startered happening as well.