While the air flow sensor is the leading cause of this code, it's important
to check to make sure you don't have any vacuum leaks and that there are no
leaks between the air flow sensor and the throttle body.
The P1128 code simply means that the ECM has to hold the injectors open
longer than it thinks it should to achieve proper mixture. Possible
causes would be:
1. Vacuum leak (especially in PCV hose)
2. Air bellows not secure on air flow sensor or throttle body
3. Air bellows broken or otherwise leaking
4. Improper oxygen sensor readings
5. Low fuel pressure (very rare)'
6. Improper air flow sensor readings.
If you haven't been there yet, there's a very nice TSB you can view at
www.hmaservice.com which gives air flow readings that relate to engine rpm
and tps values. I'd recommend looking at it if you haven't already done
so. It's TSB # 01-36-022.
If you do indeed have another air flow sensor problem, then, like I said
previously, I'd suspect some sort of contamination issue. Perhaps even
excessive engine oil entering the bellows from the breather hose and
running down onto the sensor element.