Express van rough idle and popping sound

I have a '01 express 3500 5.7L with 300,000 miles I had a hard start problem that was diagnosed as the fuel meter body defective. I changed it along with cleaning the EGR valve and changing the serpentine belt. Now it seems that on the passenger side of engine while idling, the motor is louder than before and while listening closely it sounds like maybe cylinder 8 is the culprite (small popping sound). When revving up everything sounds good and smooth. Also there was a foul smell coming from the engine area and my eyes started stinging. Could that be remnant of the throttle body cleaner I used? Any ideas? Thank you

Marc