I got a 2003 G about a week ago 86k miles 3 owners (No accid) 6S.( not my first g35 though) had a same 6s man, but got crashed.)
I went to go get an emission test and failed it? No idea why.
This morning On my way to work the check engine light came on, but before any of that starting happening the car wasnt responding to the rpm that it was showing. It would go to 4,5,6 rpm but still going 20mph???????? Then all of a sudden at a red light my clucth got stuck as i put my foot in it. And had to push the clucth back out wtf?? Then i couldnt go into any of my gears like literally!
Then i was at a hill and there was a light then out of nowhere my g35 would not accelerate i hit the gas and it would shoot up rpm's and i could see the meter going up but no acceleration??? Instead it rolled down the hill! And i could switch through the gears without even having my foot in the clucth any ideas on getting this fixed or what could be causing it?

 

From your description it sounds like you need a new clutch

 

Check the fly wheel first but it's definately your clutch or flywheel. Just had to replace mine for thI'd exact reason

 

I would definitely inspect the the Clutch Master Cylinder & Operating Cylinder operation first before suspecting a problem with the pressure plate or worn clutch. From your description, it sounds like the pressure plate is stuck in the partially or fully depressed position, which would explain the RPM increase with little to no acceleration. You could have a defective piston/ return spring in the master cylinder or operating cylinder not allowing the pressure plate to release. You have to jack up the car and inspect the mechanism while someone depresses the clutch pedal. When inspecting the master cylinder and operating cylinders, look to see if either piston appears to be extended. In theory, if you remove your operating cylinder, your pressure plate withdrawl lever should return to the normal position. There are only three bolts attaching the operating cylinder and you should not have to disconnect the hydraulic line.