I have a 2002 Toyota Corolla with check engine.

I have a 2002 toyota corolla with check engine light that comes on. After clearing the code the light still comes on sporatically. The code reader says code 0171. Bank 1 too lean. I replaced the MAF and the idle air controller with brand new units. Those 2 parts still didn't repair the problem. The fuel mileage has dropped to around 30 mpg. It used to get around 36 + mpg. Also during idle, the exhaust smells very rich and will burn your eyes. Other than that the car runs fine. The reader in freeze frame mode each occorance is different each time. The enging is always between 180 to 200 degrees, but the speed and rpm and all other specs are different before the light comes on.
One other thing with the reader when you look at the ;'self check' of each component, all components check out ok. The one reading that is ALWAYS not correct is the short and long term fuel trim at 100.6% each. I assume that it what tripps off the check engine light.
Thank you for your help.

Russ St. Germain rstg37@netzero. Net