Exhaust Sensor?

My boyfriend's Crown Vic has been acting up recently. It has approximately 114k miles on it, has had regular maintainence, spark plugs were done @ 109k. It's a '95 4.6 V8.

He says that when idling it shudders a lot, and he'll get random "Pops" which will then cause it to shake for a bit while driving. It's not giving him a CEL, and not throwing any codes. After talking to another mechanic, he suggested it may be the EGR valve. The only other thing that I can think of is that we didn't replace the plug wires and all that when we replaced the spark plugs.

Any thoughts or suggestions?

EDIT: EGR valve is what I was trying to think of. Edited that in.

If you have 114k on the plug wires, I would change them first. Ford's wires are usually good for about 80K. Try that first and get back to us.