My two cents here just to help other people. I have fixed my first CEL in my life although it was simple.

Issue: My 2001 corolla had CEL P0171 @ 95350 miles. The error is about lean fuel/air mixture which is caused by the MAF sensor also known as the air flow meter.

Solution: I went to local Autozone store and they checked my CEL for free. The DTC code was P0171 and it was cleared. It came back immediately in few miles.

Then I replaced the air filter that didn't help either. I noticed that it started giving me better mileage after this CEL kicked in.

Now it's time to clean or replace the MAF sensor. I tried cleaning the sensor first and then replace it if I need to. So I bought a one more new air filter and CRC QD electronic cleaner, then I removed the MAF sensor that is located on a big hose that connects air filter box and engine. I cleaned the MAF Sensor with CRC cleaner couple of times at 5-10 minutes interval and then re-installed it. Then I put in a new air filter immediately after cleaning MAF sensor. The CEL reset itself automatically after driving about 50 miles when the car was going up and down the hill in my area.

Please see following steps at this link that I followed. MAF sensor needs gentle hands, So be carefull and do not touch those wires inside the MAF sensor.

How to clean the MAF (Mass Airflow Sensor) in a Ford F150 (http://www.fordf150.net/howto/clean-maf-mass-airflow-sensor.php)

I have just saved about $200 for a new sensor and labor. I will replace the sensor if same CEL comes back.

I hope this would help some one.

Good luck!!!!!

LuvCamry