I installed a ztube on my 2003 g35 6mt sedan and I noticed that in neutral when I rev the engine and the rpms come back down to idle, it'll dip below idle and the car will shudder and it'll go back to idle speed. It never stalls but this is still strange. My primary suspect is the vacuum hose that plugs into the ztube is crimped (it actually is and im rearranging it soon) which causes less air to be sucked in. What do you guys think?

 

Or the maf sensor?

 

Yup, it's one of the two. Sounds like a vacuum leak to me though. If the vacuum hose that connects to the Z-tube is messed up, replace that first and see if that fixes it.

 

You forgot to reconnect the vacuum hose on the ztube

 

It's plugged in, but its so squished up that its slightly crimping when i put the z tube into place. It could be the MAF sensor getting dirt in it since that intake has never been taken off since the car was bought. I'll buy some MAF cleaner tomorrow and try that.

Also, how do I pull that rubber hose that goes into the Z tube out of the bigger rubber hose that goes into the engine so I can replace it with a new one?