I have 2004 350z with 168,000 miles. A few weeks ago, the car was making a loud noise (like it was going to blow up) as I pulled into my parking space. I shut off the car and grabbed my OBDII reader. I started the car and the noise was gone...no codes. A couple weeks later it made the noise again (very loud, car shakes, etc), I shifted into neutral and rev'd the engine to 4,000+ rpm and put it into gear and it was gone.
Today on the interstate, it happened again. Car felt like it had a flat tire, shaking and rumbling, and again the loud noise. I shifted it into neutral and the shaking/rumbling feeling was gone (but the noise was still present). I put it back into gear, the loud noise and shaking (like a flat tire from the left rear). I put it into neutral and rev'd it over 4,000 rpm a couple times and it was OK when I put it back into gear. I drive over 20-60 miles a day and some days I don't have it, but when it does happen it goes away after revving the engine...driving OK after doing that.
I have no idea how to troubleshoot this and I'm looking for suggestions. The car doesn't have any codes, doesn't lose power, etc. The idle has been a little rough. By rough, I mean the RPMs aren't consist at idle (like it'll bounce between 700-730rpm for example, but will be consist at 800rpm when the A/C is on). I replaced the MAF sensor, cleaned the throttle body, replaced air filter, and reset the ECU. I don't think it's losing spark/power because the gauges/volts/etc are OK during the issue. My guess is it could be fuel, but it's happened over three or four tanks of gas from different companies (Exxon, Shell, etc). It only started to happen ONE day after I put seafoam in the tank. It never happened before that.

 

It is difficult to discern what is actually going on from your description.

The loud noise -- where is it coming from and can you try to describe in detail what it sounds like?

Is this an auto or a manual?

You say putting it into neutral and revving it makes it go away. Does revving it without putting it into neutral or putting it into neutral without revving do anything? When it is doing this, if you leave it in gear and push the gas, does it still accelerate normally? And if it is an auto, do revs go up without the car going faster?

One thing you can try to do as a debugging step is to run the car on 5 cylinders, and see if that is the same thing.

 

It's a manual and the sound comes from the exhaust. Finally this issue threw a code, P0300.

 

Weird indeed. I found this a good read:

https://my350z.com/forum/maintenance...hooting-2.html

 

It sounds like the car is trying to stall while in gear, which would explain why it corrects itself when you take the torque off the drivetrain by putting it in neutral and gun the throttle. P0300 is a general misfire code and could be caused by a bunch of different things. Have you done any work under the hood recently? It could be a vacuum leak, bad coils, clogged injectors... All testable and if the car's never had a full tune, at 168,000 miles, probably an indicator that you need one.

 

My Z use to act the same way but just no loud nosies but the random feeling of tire is flat ( random misfire p0300) while driving and could feel it at idle. Idle wasn't steady and the pulling over neutral revving and sometimes I would turn the car off and on to get the car to run normal.

You could be lucky and only need to change spark plugs and/or coil packs . If that doesn't work you have bad rings which causes low compression in the cylinder which is causing your motor to misfire.

Now you have 3 options

1. Drive it and add engine restore to the oil
2. Swap the motor with a used oem one or LS swap
3. Motor rebuild time

I went with option 3 and made my self a platform for FI

 

Nissan said they could only get it to do it once and felt it was cylinder 6 (they were not sure what regarding that cylinder was causing it). I replaced all the ignition coils and plugs and I have drove it for about 30 miles and it hasn't happened again (knock on wood). I had a fair amount of oil all over the spark plug and ignition coil on cylinder 6. The inconsistent idle is still present.

 

I would do a compression test , swap plugs as well and then when you find out how low the compression is in cylinder #6 goto your local auto parts store and buy a bottle called "engine restore" ( 6 cylinder ) poor in where the oil goes and then drive it for about 100 miles change the oil with some non synthetic oil 5w30 and then add the engine restore again and drive it for 250 miles( make sure you let the car warm up for these 250 miles) and the. Change the oil one more time to a full synthetic 5w30 or gastrol 10w40 works really good for this senerio. And you should do another compression test and you should see a 20-40 psi jump in compression in the cylinder#6 and then the random misfire mishaps should either become rare or gone if you have decent compression already