Not sure what else to call it. Tried searching up and down and couldn't find anything helpful.

Here's the deal - I'll drive the car around some and then pull up to a light and while it is idling it makes sort of a "puff" out of the exhaust. This happens at random intervals from, if I had to guess, 0 to 5 times per second. I tried to capture the sound using my phone but you can't really hear it.

Along with this puff I am getting a vibration that rocks the engine and the transmission slightly. It is really noticeable with my hand on the shifter.

Could this be the engine misfiring? Or is there some other issue going on here? Is this common on the GSL-SE's? What should I check out first? Plugs are wires were replaced about 8 months ago, so don't think that is an issue.
The only engine mod on the car is a full RB street port exhaust.

 

yeah it sounds like ur running rich and when u come to a stop your exhaust is doing small backfires. My car does it when i downshift while slowing down luke going 45 shifting into 4th.
Is the vibration only when ur idling and getting the puffs??

 

Do the regular tune up stuff and adjust your timing. Also, once this is done you could tweak the lean/rich mixture on the firewall a bit.

Mine never does this at all.

 

Yes, I seem to only get it while idling. I have noticed some backfiring on decel occasionally as well.

Thanks, I'll start there and report back my findings.