I've noticed my 07 g35x dip in performance lately, less of a throttle response, less power etc... It's on 120000km now so what kind of tuneups can I do to gain some of the performance back?

 

Might be time for throttle body cleaning. It will restore throttle response and smooth out idle. Just be care if you diy as some people have had to do the idle relearn program afterwards.

 

Hard to say; lots and lots of unmentioned variables there.

 

Please don't. Absolutely unnecessary and causes more problems than it fixes. I would start with new spark plugs

 

^this.

Plus, yeah, what's been done to it? When was the last plug change? Air filter? Is your ebrake on? (Haha)

 

Check for a frozen caliper. I had a frozen caliper a few months back (one of the brakes was stuck) which caused my car to feel less peppy. One way to easily tell is to drive around at highway speeds for a while and then stop somewhere safe. Go around and feel all 4 wheels. If one wheel is SUPER HOT compared to the other 3, then most likely you have an issue with that brake caliper. That's how I diagnosed mine.