98 E320 make popping sound from under the hood when started
 

My 98 E320 makes a sound (popping sound as if gas is released from under the hood)when I start the car. Engine sounds little louder than normal. My wife also noticed yesterday that when she will stop at a stop light engine will rav up. Any ideas what might be wrong? Does it sound like EGR valve? If it is can somebody please tell me steps to replace it.

Thanks in advance.
Newbee2000.

I have no idea but it looked like you needed a bump.
Welcome to the forum.
Good Luck, Dan

Thanks Dan, I took the car to the dealership and they hooked it up to the dignostic machine and could not find anything wrong. Service adviser mentioned that it might be Trottle positioning sensor going bad and it is about $1400 part so he did not want to change it right now. Is it hard to change this part? Is it really that expensive?

Thanks.