[fredjacksonsan]

Lean mixture is all I can think of; how is your air filter? On older cars with carbs, a clogged air filter would cause a rich condition; however on fuel injected engines the reverse can be true. You might want to check/replace the air filter, and check the intake for any buildup.

How about some fuel injector cleaner? If the injectors aren't bringing enough fuel to the cylinders, it could cause a lean condition (assuming the computer can only adjust so far)