Car Farts

OK, so sometimes the rental car makes a fart smell. It usually happens when I have to, like, rev the engine because I'm stopped on a hill and I want to get going without rolling backwards or stalling the car (I still usually stall out). I don't know if this is a diesel car thing but I'm guessing it is since both of the rental cars we have had did this and they were both diesels.

So this happens last week with just VJ and I in the car and the conversation went like this:
VJ: "Ewww! Stinky!" Covers nose with hands
Me: "Yes, the car is smelly."
VJ: "No Daddy. It's not the car, it's you."
Me: "No VJ. It's the car."
VJ: "No, it's you. It's your heinie."

The kid would not believe that the car had farted and not me. It's happened twice more and he always blames me.