What could cause high boost reading/bad gas mileage
Monday morning while driving to work, I noticed my boost gauge was reading about 10-15 lbs of boost higher than normal. For example, when going up a slight hill, it usually reads minus-10 lbs on the gauge, and it was reading +5 lbs of boost.
The engine did not seem like it was laboring any harder than usual, but I burned about 2 times the usual amount of gas going to work and back. I was just driving along with traffic, not accelerating fast or anything. A 42-mile round trip, combination city-hwy.
The next day, it acted completely normal, with the boost gauge reading like it should and the gas mileage going back up to normal. Since then, I have reset the ECU and re-flashed.
Any ideas what would make it temporarily show way-higher boost and burn up twice the gas ? I eliminated things like parking brake engaged, foot on the brakes.
'09 WRX, Catback, Cobb Stage 1, no other power mods.