2008 350z problem
So this car has 170k miles
on cold start it sounds like it about to die for a few seconds you’ll start it up and some days it’s worse than other but I’ve noticed it’ll get down to like 250 rpm and sounds like it has somewhat a cam and then it’ll shoot to 2k rpm after a couple seconds

If you shut the car off and start it when it warm it’s perfectly fine I feel like it could be a sensor but it’s not throwing a sensor code
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I also posted about this 2 weeks ago and haven’t figure out the issue so I’m posting to maybe get someone else to see it I’ve tried cleaning both maf’s and also checked around for air leaks with starter fluid

Another thing is we did an oil change on it and it started up fine and my girlfriend said it starts regular for like a couple days after an oil change and then goes back to how it usually is

 

Questions…

what oil did you put in the engine?

does this only happen in cold temperatures?

When was the last time you replaced the cam shaft and crank shaft position sensors?

when was the last time you cleaned the MAF sensors?

when was the last time you did the throttle body relearn procedure?

 

I don’t think it matters the temperature only when the car is cold if the car is warmed up and you turn it off and back on it starts completely fine

we used valvoline 5w-30 full synthetic high mileage

don’t know when the last time the cam and crank sensors were replaced or if they have been replaced in general

I cleaned the maf sensors almost a week ago with no change

I did not do a throttle body relearn and do not know when the last time it was done or if it’s been done

 

Good info ...

They rarely go out but if you can check (some how, not 100% sure with your setup? possibly with an OBD2 scanner that provides live feedback) check the engine coolant temp sensor - it's located in the back of the engine and isnt completely impossible to switch out but test it by looking for live data from an OBD2 or if you have tuning software on your car you can sometimes get a data output. Like I said, doubtful this is the cause but seeing that this problem only occurs when the car is cold it would be a good thing to check off the list. Further - a bad ECT data input isnt really going to make the car that much more difficult to start. But check it off the list.

5w-30 is fine just wanted to make sure you didnt have some crazy thick oil in the car.

I would replace the cam shaft position sensors and the crank position sensor. Very important to only use Hitachi Brand or OEM Nissan from the dealer. I would buy these locally or from a trusted website (Z1 or Concept Z) as alot of sellers say they are Nissan and they are knock offs. Hitachi is probably the best bet - I cant remember what other sensors you have on the front of your timing chain case but it may be wise to replace them especially if you dont know the last time they were replaced. I order them online from a trusted local auto parts store (advance, Oreilly's, Autozone and use their promo codes to save a little cash).

Good stuff on cleaning the MAF - good practice to check and clean it every 5k to 10k miles.

Do the throttle body reset - just google it and you'll see the instructions. You could do the acc pedal relearn too if you wanted.

 

Have you gotten a lean bank one or two code at any point?

I have a 08 that did that for a few years, had a slight stumble right after it would Rev up on start up then go to a steady idle after a second or two. Turned out to be my fuel pump.

Only recently it started throwing the codes making me think there might be a pump issue. Went away after.

 

there was a lean bank 1 code but cleared it and it’s been away for while now

 

Those symptoms are in line with a vacuum leak. Spray carb cleaner around the engine to see if revs increase. Or the real rest is a smoke test if you have access to one.

 

o2 sensor just needed to be spaced out from high flow cat because the high flow cat has become less efficient