Need help please 2001 Firebird V6 M4 poor fuel mileage/misfiring

(AUTOMATIC, sorry not M4.. Who makes an M4? :-p )

Anyway my friend is having a problem with his 2001 Pontiac Firebird 3800 Series II V6. It has 39,000 miles and has been maintained at the dealership since it was new. It is the automatic. He's recently had the dealer perform the major service/tune-up and since january has been having POOR fuel mileage (140 miles per tank -- if lucky-- per tank) I notice the engine runs rough or "lumpy" at idle...(maybe I'm used to my 2006 3 series engine haha) so I changed his plugs and wires for him.. yesterday.. we dont know if the problem will go away.. the old plugs and wires appeared pretty shot. I was thinking its the coil packs? He took it to AAMCO when he first started noticing the prob and they told him he had cylinder misfiring (not sure how many or which ones) but I dont see any check engine lights. My research tells me the older 3800s had this prob, but on a 2001 with only 39k miles!? Not to mention his fuel gauge needle fluctuates a LOT.. we'll sit there and WATCH it move up and down + or - 1/4 a tank

I think I'll target the coil packs next. Any ideas? MAF maybe? (and SORRY THE TITLE SAYS M4, I MEANT A4 automatic)

It would help to get the car scanned and see if it is a general misfire or a cylinder specific misfire.

I find it hard to believe that the plugs would be bad so soon. I'm with you on a coil pack. It would really help if you had a trouble code to go off. Did you try running it in the dark and looking for a spark misfire under the hood?

No, I assume just pull the plugs and watch for sparks at the top of the coils? They won't arc off eachother?

You need to get the car scanned to figure out what cylinder is misfiring. I can Get 230 miles out of the first half part of my tank. So there is something very wrong. Could be a coil pack. Could be the MAF. You wont know until you get the car scanned.