I started up the Z a few days ago and it started off idle-ing at 1600 rpms! Its never jumped that high before! Its always been at around 1250-1300. Needless to say it scared the hell outta me when I turned it on. It still is turning on with slightly higher rpms, but not as high as a few days ago.

Any suggestions as to what it may be?

 

Does this happen just when the engine is cold, or is it all the time?

 

Just when its cold, but like I said in the 10 months Ive owned it, its never started idle-ing that high before. And now its not having a steady idle when im stopped and in Drive. It goes up and down....starting to remind me of my Eclipse....

 

Sounds like a vaccum problem if it's going up and down after it's at normal operating temp..

 

That would do it, and has done it to me once or twice in the past.

Also possible that there is a dirty sensor somewhere and ECU is defaulting to a higher rpm because it can't accurately measure something. I had this issue in my truck after adding a K&N filter with a bit much oil on it. Didn't so much notice the rpms going up (5.4 Triton + automatic) but I did notice the mileage drop to about 8 around town.

 

I just added a K&N filter as well. Well Im taking it to the shop soon to make sure nothings seriouse is going on.