So lately I've been noticing that my RPM needle bounces up and down around 1,800-2,3000 RPM for the first couple seconds upon startup and then slowly goes down to resting idle. This is my second G35 and Iv'e never seen this happen on my old one and didn't happen in this one utill about a month ago. Has anyone else had this problem?? Btw its been really cold lately and I've been noticing crappy gas mileage.. Don't know if that has anything to do with this issue. I will try using Seafoam this weekend to see if it helps. Any ideas?

 

bump!

 

Could just be the cold weather, but check the throttle body and MAF...they may need to be cleaned. Also, try doing the idle air volume relearn procedure.