Check Engine Light and weird revving of engine
 

Hi all-

The check engine light came on last night on my 2007 Passat, and it has been idling very low (700 RPM). Also, when I have it in park and rev the engine up a bit, once I take my foot off the gas, it only goes down to about 1500 RPM, and then revs itself up from 1500 to 2000RPM on its own over and over again (without me touching anything).

Do you have any idea what might be causing this?

Also, I assume whatever it is would be covered by warranty (it is a lease with 16K miles), but wanted to make sure that if I brought this in, I would not have to pay to have it looked at. Anyone know about that?

Thanks!