I have a 04 Automatic 350z and bought it recently knowing it had this issue but it’s gotten worse and i want to find out whats causing it.

when it’s cold it does this once and only once, it shifts normally but then in like 3rd gear it shifts into it and then revs as if its in neutral for like 0.3 seconds and then drops and operates as normal, yesterday i was playing around with the manual mode features and i guess i forced it too much and the car supposedly was in 4th but it would free rev like in neutral until it hit 4000rpm where it then started to move, so it would just not do anything until 4000rpm, sometimes it refuses to go into manual, just stays in drive, and the weird thing is my mechanic told me the transmission feels fine and he wants to take a look at the valve body first so im kinda confused, it also has a spark plug issue where the engine sputters but only in gear, in park or in neutral nothing happens, any clue what you guys might think it could be??, anything helps thank you!!

 

First things first. Read or get OBD codes read for you. Caveat: Not all shops have the correct scanner to read Nissan (or whatever mfgr) transmission codes. They (or you) will require a scanner that has MSDC or multi-system diagnostic capability. That being the case, you should find out BEFOREHAND if the shop you're thinking of bringing it to has this capability. Because of this, I would recommend taking it to a transmission specialty shop OR a Nissan specific shop that likely has the proper scanner for A/T codes or Consult 2/3 that is used by and for Nissan specific vehicles. Just as an example, all 10 of my technicians have their own scanners but only my two Master Techs have the full on machines. So, ask first..

Purpose of pulling codes is to give the tech and customer a "GENERAL" idea of where to focus the diagnostic. General because while a particular symptom may, 8 of 10x, be the first DTC (diag trouble code) found but there's that other 20% that it could be.the issue. Again, a transmission or Nissan specific shop is your best bet.

Next, a basic question: When was the fluid last changed? People tend to neglect this on a routine cycle every 20-25k miles and things start to get gummy inside. Valve body, solenoids, bands, clutches, etc all like fresh trans fluid. In the case of Nissan, use OE fluid, Matic-S. Ask for it or pretty much the only alternative, Castrol Transmax. Don't believe any shop that says "Oh Dexron VI (or Mercon or Type F or others) is just fine." Yeah, might work in a pinch but at the possible risk of misshifts, sloppy shifts and possible damage resulting from improper fluid pressure if the ATF used is a different density. Again, this is pretty worst case but why risk it?.

S'far as the engine miss issue, it sounds like it only happens under load so that points to ignition or, IMO, more likely, fuel issues. Bad fuel (low octane, moisture in it, just low quality) can easily cause this. On the ignition side, could be as simple as needing new plugs or possibility of a failing coil or two. Again, a code read might help to narrow this down.

 

for sure put a proper scanner on it. Regardless I would change out the transmission fluid and spark plugs. At the end you really dont know if they were ever changed.