It goes up and down for a minute then settles. Do you know whaat might cause that?

 

Might try cleaning your MAF sensor. Has it always done this or did the problem just develop?

 

Need more info. Is this at startup? After it has run and is hot? More details man!

 

Could be a vacuum leak, check your intake connections!

Tim

 

factory airbox is very constricted..also has a filter you don't see in the elbow part going to throttle body..

 

Only the early 05's have that extra filter in the elbow. We don't even know what year car he has, he gave no info at all about his car or his situation.

 

That's a very limited question....

Dirty MAF?
Cold weather start?
Higher than average idle?
Leak?

*To OP: Colder weather yields higher rpms @ start-up. Mine sits @ 1K for about 5-10secs and levels to 750 (tuned).

 

my money is on a dirty throttle body.
clean up the carbon/oil build up on and around the throttle body plates and you should be running fine.

 

I would clean the TB and MAF sensor.

That thing in the intake elbow on the early '05's was a device used to trap any unburned fuel vapors that may try to escape to the atmosphere through the airbox....emission control device.

 

I've got an 06GT... does the exact same thing. Right after starting, RPMs go up and down rapidly between 800 and 1200, but only for about 30 seconds, then it settles down to perfect idle. Did it when I had the stock intake on.. and does it now after I have my C&L street intake on. I've checked connections, cleaned TB & plates, cleaned MAF sensor... no affect... still oscillates between it's narrow band for 30 seconds, then all is good. Post if you solve the mystery.

 

Like the other guys have said, we need more info.......including what (if any) mods you have on your car.