Hello, I have a 2008 Base, manual 350z with 68k miles on it. Ever since I bought the car it has had this problem of RPM drop on start up. If the car is cold it will not happen only when it's warmed up. It's never been a real problem as it doesn't effect the car in any other way, just getting a little annoying. When car is warm during start up the RPM will drop down to about 200-300 then shoot back up to normal 700ish idle. Happens 90% of the time, the other 10% of the time it starts up fine with no RPM drop. I seen some post on this forum about it but the problem, from the ones that I have read go unsolved.
No codes are thrown either.

Here's a link to my car showing the RPM drop

 

double posted by mistake

 

Ever cleaned the throttle bodies? That's usually what causes problems like this.

 

mine did that ... wouldn't worry about it