RPM's up and down at idle
 

I am new to the 350 world because i just bought a black 2003 Enthusiast, 6spd. last month. It only has 50,000 miles and clean title. Yesterday i turned on my car and had it in neutral of course and while i was deciding what CD to listen to discovered that the RPM needle was moving up and down. I say from 250-750 RPM's. I also heard a clicking noise coming from the engine bay. I talked to a friend of mine and he told me the same thing use to happen in his EVO and discovered he had a bad sensor. If someone can direct me as to what steps i should approach first that would be better than taking it to NISSAN $$$$. Any help with my situation will be much appreiciated. Thanks.

Wow, your friend is a wealth of information! I once had the RPMs hunt like that, and it turned out to be a vacuum leak. Are there any mods on the car? Do you know anything about its history? Is it throwing any codes?

The only mod i have is an Injen CAI. The only history i know is that it has 2 previous owners. I think i'll start by taking it to AutoZONE and have them hook up diagnostics on it. You have any other suggestions??

Yes, I do. The only diagnostics Autozone can run will be if the engine is about to, or already has thrown a code. They do not nave a Consult II. For that, you need to go to Nissan. My bet is on the CAI. Dollars to donuts, if you put on the OEM intake, you will eliminate the RPM issue. That has been discussed here before, but I don't remember if it was a bad installation, a leak, the MAF, or what. Use 'advanced search' on Injen CAI. If you don't have the OEM box, someone here may have a revup box which will not only fit perfectly, but it will make you forget all about the Injen, performance-wise. Good luck!

Vacuum leak or Idle Air Control (IAC) valve is faulty. Definitely take your car to autozone and see if there are any codes that may give you a better idea of what is wrong.

my 2004 Enthusiast, does the same thing. doesnt bother me.

Mine does the same thing every-now and then... i was always told they just do that sometimes....I wouldnt worry with it unless a check light comes on...

I feel sorry for you guys, but apparently you don't mind or care. What kind of car did you drive before the Z that would make you think that this is okay? No, I can't fix it for you, and it may or may not be worth fixing, but rest assured, it is NOT suppose to be like that. I've owned mine for 3 years, and it has never done it, FWIW.

I believe mine did that after replacing the battery... It didn't keep doing it though - just 1 or 2 startups. Then it "learned". I have a reflashed higher idle set - so I thought that might've had something to do with it.

If you have a CAI check and make sure all your gaskets are tight. MAKE sure you check the vacuum tube that lies underneath the upper tube, you cant see it right off hand. If thats all fine, then like others have said in this thread you may need to perform a Idle air learn. I believe you need the consult 2 for this, I dont know of any way to initiate a idle learn manually without the diag tool.