sup guys/girls. im having a problem with the car that mechanics cant figure out. at idle the car has a very high exhaust smell. the exhaust sputters alot like a mis fire but all cylinders are firing and i have no cel. also when i put the car in drive the idle drops (normal) but i get alot of vibration and fluctuation up and down of the rpm. i have checked all vacuum lines and anything else that i could think of that can affect idle. anyone have any suggestions that maybe help me resolve this annoying matter. thanks in advance for your help.