Toyota: Toyota celica 2000 engine light, mass air flow sensor, mass air flow

Question
I have about 73, 000 miles on my celica.  My engine light came on. I had a 3 step fuel injection system clean after the first time and it stayed off for just over 1 month.  Now it came on again.  I had them run the diagnostic test both times and came up with a "lean" code (PO171) both times.
The car seemed to hesitate when accelerating after the first time but now runs normally.  
Perhapsy my O2 sensors need replacing?


Answer
Hello,

The problem could be:
- Lambda Sond
- Catalysator
- MAFS (Mass air flow sensor, placed after the air filter on the intake hose). Sometimes the mafs is only dirty. But be carefoul when you clean it, it's very easy to break it.

Regards,
Jack