It hesitates when it happens, but other that that, gas mileage is good, cruising there's no noise or issues...

I'd still search for vacuum leaks -- if more air gets sucked in than is measured, it will run lean and attempt to correct with fuel trims; that could cause the running rough and hesitation issues.

Nissan says that because what you cleaned is not the fuel filter. That is the fuel pump pickup. It has a rough mesh to prevent large debris from entering the pump which could damage it or jam it.

The fuel filter is insert molded into the fuel pump module. If you notice how your fuel pump has a black hose coming out the top of it, which then turns 180 degrees back down into the fuel pump module. That is the filter, and it cannot be replaced or serviced as you cannot open the molded housing.

Generally, you dont have to worry about that filter for a VERY long time.

The rule of thumb for fuel injected cars is to get about a 100 micron mesh before the fuel pump, to protect the pump. After the pump, you want a 10-40 micron mesh filter to protect the fuel injectors.

Update:

I pressure tested the intakes/plenum and found a leak, it was the passenger side breather that goes to the valve cover (I have K&N Typhoon Intakes) Needed some thread seal tape. Also looked at other K&N installs, and the previous owner left on the baffles/sound dampeners, which after reading the installation instructions I downloaded, K&N says to remove, so those are gone, ordered the z1 motorsports replacements.

Changed the oil with Mobil 1 Synthetic 5w30 (I was using conventional 5w30 the last 2 oil changes since I got the Z) and the violent valve/chain/whatever noise now rarely happens, as does the slight hesitation related to it. I'm wondering if the hydraulic chain tensioner was stuck from the thicker oil, causing the chain to slack and the timing go goofy?

I still have the odd issue of when I'm accelerating at a normal pace (not WOT) it'll just drop RPMs like before, but not as drastic as before I fixed the intake leak, only 200 - 300RPM.

Spoke too soon...

It's still making that awful noise, only when in gear, only when from a stop, only when I slowly accelerate, and it still hesitates when it happens. Give it more gas, and it catches up with itself. But, still, intermittently.

I re-pressure tested the intakes after I installed the Z1 Motorsports breather tubes, and there are no leaks, also got under the car, and except for a small leak at the passenger side muffler (that I was able to tighten and fix) there are no leaks at any of the other flanges, no leaks at the 02 sensors, and no CEL or codes. Even when the issue occurs, there's no CEL or other warning light.

Gas mileage is good, power at WOT is good, and no other weird noises.

I'm at a loss on this. :shakes head:

Did you check the mafs? We had a,civic run like crap, because it caught a small bug on the sensor, probably not it but worth a shot.

YYYep, I used that CRC mass airflow sensor cleaner, also did the idle air learning procedure just in case.

Seafoam? Id do a, can in the gas and intake..cant hurt at this point

Did that too lol, I actually just ran that tank that I put the Seafoam in down to E and filled up at BP

I'll try it through the intake tomorrow - you mean the brake booster vacuum tube?

Ya that will clean out manifold and lower collector again cant hurt, but this one seems beyond my diagnostic skills at this point im just guessing at this point to be honest

Yeah I'm completely lost.

Just a shot in the dark here but try checking the transmission mount. I say this because I had very similar symptoms in my sisters jeep. It rattled in gear and during acceleration but not when cruising. Luckily it is pretty easy to take off and inspect... or just upgrade to the Z1 unit while you are at it.

It might help to do some parameter monitoring and/or logging.

You can find cheap ($20-40) ODB/CAN-to-USB convertors on the Intertubes and there are several free programs available. I have a page that lists/reviews some of the programs at the link in my sig.

If you have an Android device, there is an app called Torque available.

If you need to dig deeper than what the above can handle, one of the tuning apps would be an option.

I actually have one, I'll post some data logs soon...