kevsgt

After a 20 mile drive, slowing down to a near stop I felt my car seat shaking. This continued when I parked the car, pretty violently at times, and random. I cleaned the TB and the MAF, waited 20 minutes then drove some more. The car started doing it again. I looked at the harmonic balancer, because one of these forums pointed at that as a possibility, but didn't see any wobbling on it. I took a video of the engine, and you can hear a strange thwumb in the video twice maybe 10 seconds apart.

The car sat overnight, and no longer shows signs of the rough idle...

Only other tidbit is that this happened the same day I got my car back from the body shop. They installed my newly painted hood that morning or the day before.

I checked today and the car is throwing a P0316 code (misfire at startup), even still, although no rough idle at the moment.

99GTvert

How many miles on the car? What/when was maintenance done on it?

kevsgt

125k on it now.

Recent work:
At 120k, I replaced the fuel filter.
At 100k, shop replaced some of the spark plugs.

JimC

"Some" of the plugs? Why not all of them. That could be the source of your shaking. With 125,000 miles on the remaining plugs they are long past time for a replacement.

kevsgt

Sorry, they were all replaced. Just some of them had broken coming out, is what I was remembering.

I'll also add that I have aftermarket BBK CAI and TB from many miles ago.

Derf00

I'd be checking out the air intake. Check for any loose or broken hoses going to the intake after the MAF sensor. Also, the general consensus on aftermarket TB's is that they are junk. While they may not have problems for a while, they do tend to fail which leads to all sorts of strange problems including throwing codes, idle or under throttle problems, etc.

Do you have the OEM TB to try out?

techguy

Put some HEET in the gas tank run that out. Then get $10 worth of gas from a very busy brand name station get midgrade and add another HEET treatment.
Maybe you have to use a injection treatment as well

kevsgt

the rough idle has not come back since that 1 day. maybe cleaning the MAF fixed it, just took some time to go away.