P0174 OBD Trouble code

I took my 2000 Ford Winstar Van to the emmission testing facilty after the check engine light came on and the test indicated the following OBD trouble code: P0174. I have researched the code and in summary it appears an oxygen sesnor in bank 2 detected a lean condition (too much oxygen in the exhaust). Prior to reading the posts on this fantastice website I was under the impression the error code is usually related to the mass airflow sensor (maf) or vacuum leak downstream of the sensor (according to obd-codes.com). I cleaned the maf (with air), repaced the air filter, unhooked the battery cables to reset the computer. The check engine light did not show its ugly face for 3 weeks but it is now glowing. After reading the posts on this site it would appear to be a vacuum leak? If that's the real problem why wouldn't the check engine light come on much sooner. Is diagnosing a vacuum leak something a laymen like myself can do or am I I better off just taking in into a mechanic.

The computer needs to detect the fault a few times before it illuminates the CEL to ensure that it is not a glitch. Perhaps your vacuum leak is just at the early stages and is quite subtle and just the right (wrong?) conditions need to exist before it is detected as a fault.

It is not unusual for a failure to take a couple of weeks to illuminate the CEL.

your vehicle has a technical service bulletin for intake gaskets,bolts,possible left hand valve cover,fuel pressure regulator hose and pcm reprogramming for lean codes; this does not mean warranty will cover the cost