Hello,

Car History
So i purchased my 6-speed g35 about 8 months ago. It had about 42,xxx miles and now it has 58,xxx. I have changed the oil and everything and taken good care of it. The only thing which I have done is hit a curb going about 5 mph if that. It seemed like no damage at all - other than that no issues or anything wrong. I also put a 350 Z-Tube in with a K&N Filter

Issue
I put the intake/filter on about 2 months ago, then about a month ago I 'thought' the car did not pull as hard as it used too. Before if I got on it from 1st with traction control off it would kick the rear end out. Now it does not really even chirp the tires. It seems like low end has lost some power (not significant but it seems noticeable). The top end seems ok, maybe not quite as quick but no real loss of power is noticeable so I can’t give a definitive answer on that.
About a week after I noticed that the acceleration has decreased I also noticed a slight 'fluttering' sound coming from the engine area. The noise is not heard below 3,500 RPM. I do not hear this sound every time, maybe only 60 % of the time. If I hold the RPMS at 4k the noise is sometimes constant. It is very faint and kind of sounds like a flutter - like plastic or a cover or something. It does not really sound metallic like a bent valve or anything like that. The sound seems to come from the middle of the engine it seems like. I can’t pinpoint it. Sometimes I think it comes from the right side of the car then others I think from the middle. My friends also say the same thing.

note
- The Z-Tube was tapped for n2o. I plugged it with a plug and tape. I think this may be an issue has the intake may have opened up again, any thoughts?
- My car gets good gas milage 350-400 every tank.
- I have not noticed any oil burning. Everytime I change the oil (at about 3-3,300) miles it seems to only be about a 1/2 to 3/4 of a quart low. So it isnt really burning any oil.
- Also, my co-worker purchased a 06 auto G35 (coupe), and honestly I believe his can pull away from mine.

Any Help
Any help would be appreciated. Like I said, it feels a bit slower, mainly on the low end. Also there is a slight fluttering sound from the engine.

 

First thing to do is check that plug. Try cleaning your MAF sensor as well.

 

if you can, put your car on a lift and check your Ypipe and other exhaust parts for a leak. For me, when I heard the fluttering sound, the flex area on my ypipe had broken. hope it's something better for you but at least i hope you find out.

 

Reinstall the old intake tube and see if the problem goes away. Make sure all fittings and clamps are secure. The smallest vacuum leak will create all sorts of driveability issues.

 

Thanks! I will put the old Intake on and see if it fixes it.