I have a 2001 Porsche Boxster 2.7L with about 55,000 miles on it. Recently I have been getting CEL for P1128 and P1130. I have an ODBII with some recording capabilities and was able to record a driving session with STFT for both banks. I looked through the data and for the most part it is within the +- 10% mark. LTFT was set to +3.3% on both banks. What I found in the data that was very interesting is that there are short spikes of -99% trim on both Bank 1 and Bank 2. This only occurred once on each bank over a 20 minute drive
I believe this is what is causing the P1128 and P1130 codes to occur. I just don't know why the trim would spike to this for short times. Below is an example of the data:
LTFT1 +3.3%
LTFT2 +3.2%
TIME STFT1 STFT2 MAF Air Flow
115.5 -3.1 -3.9 0.73
115.953 -3.1 -1.6 0.73
119.297 -3.1 -98.4 0.73
119.703 -3.1 -98.4 1.92
120.094 -0.8 -98.4 1.92
120.5 -0.8 -2.3 1.92
120.891 -0.8 -2.3 2.08
121.297 -3.1 -2.3 2.08
122.594 -3.1 -5.5 2.08
124.391 -3.1 -5.5 2.55
......
768.453 1.6 3.9 1.49
768.797 2.3 3.9 1.49
769.141 2.3 0.8 1.49
772.203 -98.4 0.8 1.49
772.5 -98.4 0.8 1.49
772.797 -98.4 0.8 0.6
773.094 -0.8 0.8 0.6
773.453 -0.8 -2.3 0.6
773.797 -0.8 -2.3 0.56
774.141 0 -2.3 0.56
774.453 0 0.8 0.56
The car does not run poorly in any way. Here's what I have tried so far from suggestion in this and other forums to resolve P1128/P1130:
- Replace AOS (replaced 2000 miles ago for unrelated issue)
- Check Oil cap for air leaks
- Clean MAF sensor with MAF sensor cleaner (engine runs more smoothly now)
- Check air filter (replaced 2000 miles ago)
- Checked for disconnected vacuum hoses
- Check that oil cap seal was not leaking
From the chart above, it seems like the MAF is doing its job. Perhaps there is some faulty wiring that is causing a short to battery or short to ground causing the intermittent spike. Has anyone seen something like this before, or have any ideas what could be causing it.