At first I thought this was a issue with the steering, but now it has become clear that this a miss/hesitation.

It does it only on my 1-2 or 2-3 or 3-4 shifts at 1/4 to half throttle the most, sometimes even under WOT. Not that I can recal has it done it from a stop light. Right after I shift and I get back on the gas, it will feather in and out about 4-5 times before running smoothly again, almost like its missing? No CEL'S or lights. (see sig for car info)

The idle is less than perfect but nothing severe. It just kinda jumps around 150 rpm or so. Also when I shut the car off I get this hissing noise, sounds like presurized air being relieved slowly, but its coming from under the hood (around the airbox/TB). It continues to make noise for 15-30 seconds before slowly dying to nothing.

 

Any tune ups performed???

The hissing, are you running your A/C then shutting it off? If so it is normal after turning the car off.

 

I dont know about tune ups as I just got it. I was just wondering if this was a common problem. I'll replace the plugs and try again. I run only V-power 93 octane, btw,

 

I would really check the plugs and normal items first. Also and I have been nagging about this. Cleaning the throttle body and iac valve including the pcv tube thing that runs under the throttle body. I fully believe this should be done before 90k.