My "check engine" light came on...help!

I have a 2001 IS300 with 35,000 miles, the car has always been pampered....the other day I got in my car to go to work and the check engine light was on! I freaked! I looked in the manual and it said the car could be out of gas or the cap not tightened or fuel injectors....well, the gas cap is tight and the tank is full....the car runs excellent, not sluggish or anything, could I possibly have some bad gas? Please help if anyone knows. The car is still under warranty but the closest Lexus dealer is 2 hrs away. Any ideas or suggestions would really be appreciated. P.S. The only modifications I have is 18" chrome mashie wheels.

I have a 2002 IS300 5-speed with the HKS Air Intake and Cat-Back Ti exhaust (and other stuff). At 32,000 km (about 20,000 miles) the "Check Engine" light came on. The Lexus tech said the Air Flow Meter may be faulty, so he replaced it under warranty, but warned me that the after-market air intake may be the culprit, so any further repairs related to it would NOT be covered. Anyway, the light went out for a few days, but then came back on. Anyone else had this problem, even without the aftermarket air intake?