I would still check the MAF though.

It should be totally clean. If you notice any oily residue on it, its time to clean it.

 

If you hear a hissing noise, I would recommend you to loosen everything and retorque them according to the given specs and sequence from Motordyne Egnineering (becareful that the Oil Filler tube's flap won't get trapped in between the spacer and the plenum).

For the temperature factor, I totally agree with Tony's argument.

For a piece of mind, if retorquing the spacer doesn't help, try clean the MAF with a proper MAF cleaning agent.

 

Hahaha! Godmans you live in Canada so you got that extra TQ almost all the time!

 

Alright guys, did a number of things today:

1) I reconnected the vacuum lines on the intake tube and plenum (they both looked fine though).

2) Checked the MAF sensor, clean as a whistle, no oil residue.

3) Checked the 6 main bolts on the plenum and discovered a few things...

The 3 bolts in the front were all loose, it took almost no effort to remove them. Also, looks like I somehow forgot to install one of the washers on a long bolt (in the back). I used a spare washer, added a little more loctite than last time, and retorqued the 6 main bolts. I torqued them to 40 inch-lbs, then I torqued them to 84 inch-lbs (slightly more than the recommended 80). I let the loctite cure for 3 hours and started her up. Idle is a little bit smoother, can't feel any vibrations on the steering wheel now. But there is still a slight hissing noise. I stuck my head in the engine bay and narrowed down the location (circled in red in the attached pic). It's definitely not the belts, the two sounds are distinct. I took the car for a spin and it feels more peppy. Not as much lag when I hit the gas from a roll. So I guess the million dollar question is...given everything that I did, is that hissing sound normal?

 

That is where the hissing sound always comes from. Its the cam advance hydraulic system.

 

Beautiful. I feel like an idiot, but now my mind is at ease! I think it was still worthwhile to do the troubleshooting. My hope is that the extra loctite and torquing to 84 inch-lbs will keep everything tighter. Thanks for all the help.

 

Pleased to read that you were able to resolve the issue(s). Now, go out and enjoy your G.