LS1 Vibration

[02BlackSS]

Hello all,
My 02 SS M6 w/9000 miles has seemed to develop a vibration. I don't recall the vehicle having it until I installed a Flowmaster Cat-Back and a K&N filter in the stock airbox. The vibration seems to be primarily from about 1800-3000 RPM, then smooths out above that. I was thinking clutch components being unbalanced, but wouldn't that get worse with RPM? The car has always had a shake at around 1800 RPM if you push in the clutch or have the car in neutral and free-rev the motor. The tone of the exhaust also sounds like maybe a cylinder isn't firing quite right, but there are no SES codes or lack of performance. Any advice you could offer would be great. Also I heard something about the stock plugs losing their platinum, thus increasing the gap to an unreasonable amount-is this possible, and if so, possibly the culprit?

Thanks!

[Jay 02 TA ws6]

Hmm... a vibration that you feel, or a rattle that you hear?

When I did the Corsa cat-back, I didn't give the over-axle pipe enough clearance, and at certain times, the pipe would vibrate against the brace and cause a hellacious rattle that vibrated the car... any chance that is it?

[02BlackSS]

More of a vibration that I feel. Oh, and I know what you mean about the exhaust rattle-I had that, too, until I went through and got rid of the clamps and welded all of the joints-so I know it is not the rattle. Thanks, though. That is a nasty rattle when the pipe hits the suspension...

I am almost positive the vibes are from the motor or other drivetrain parts, because of the way it feels. I can feel the vibe in the shifter and accel pedal.

I forgot to mention, my gas mileage (maybe unrelated) has really been poor. I only get about 20 mpg on the freeway with the M 6 and 3.42 gears. From my understanding, these cars should get about 25-27 freeway. Am I wrong on this?

[Jeff_in_Atl]

This may seam dumb but I did this dumb thing once before. I didn't get the hose to go all the way on the MAF. It was sucking in un metered air. It ran like crap. It vibrated too. I'm sure it screwed up the gas mileage too. I have a hard time getting the elbow to go onto the throttle body on mine.

[Jay 02 TA ws6]

I have ALWAYS experienced vibrations in the shifter and gas pedal. Ever since the car was brand new. The gas mileage is another story. I saw 29 mpg when I came back from Bowling Green, Kentucky earlier this year. That was going 65 mph the entire way... I see a big drop off when I cruise at 80 mph... BUT -- I am running super rich right now.

EDIT: I too, have the M6 with 3.42 rear.