High RPM / Sticky Throttle
 

I have a 2006 350z Touring with a manual transmission and 170k miles on the odometer. I have been having this problem for about 2-3 weeks now. I know that cars idle high on startup to get the engine warmed up; however, the rpms tend to stay around 1.5-2k whenever the car is out of gear even after running for a bit. For example, when I was coming to a stop the other day, my rpms will come down fine in gear, but will jump to around 1.5-2k whenever disengaged.

I'm not sure if this issue is related, but whenever I take my foot off the accelerator the car seems to jolt after about 1.5 seconds then proceeds to decelerate normally.

I may be wrong, but I think it may be a problem with either the throttle body, or a vacuum leak somewhere. I would greatly appreciate any help in the diagnosis of this problem.

Because this car has a "flt by wire" setup it could only be the butterfly sticking, but that's not likely either (I'd imagine there is a limp-mode safeguard and MIL for that). If you've done any recent maintenance, I'd check for air leaks. The car has a ECU controlled idle so it will try to hit the target regardless of other issues, but that too could lead to over-compensation.