I am having intermittent P0172 & P0175 codes (too rich on banks 1 & 2). They show up when I have less than a half of tank of gas and when I slow down from high speeds or stop at a light. The OBD data shows at idle short term fuel trim -15 to -20% on banks 1 & 2 and ~-5% on bank 3 and ~ 5% on bank 4. Long term shows: -20.3%, -7%, 3.9%, and 0.8%. At 1500 to 3000 rpms, short term are: 12%, 14%, 21%, and 24%. Long term are: -12.5%, -8.6%, -3.1%, and 2.3%. When the banks run rich, it shows in the O2 sensor data. Any thoughts on what the problem is? Also any idea where the banks 1-4 are and where they are measured?

 

Welcome to the forum, you've come to the right place. There is a lot of good information here and quality people to help you diagnose and repair problems.

You've doe a good job in providing scan data and are on the right track with Long- and Short-term fuel trims as a diagnostic aid. Yours is not a unique or difficult problem, most likely the Mass Air Flow Sensor (MAFS) going bad, an easy DIY fix.

If you make a few more posts you will earn rights to navigate this site fully and can access the JTIS files (technical data by year) and more.

In the meantime someone will chime in and get you started.

Welcome aboard.

 

I cleaned the air flow sensor with crc cleaner. Now I am a running lean. It should be noted also the daytime temperatures have been 15-20 degrees warmer. I plotted the rpms with the MAF data (g/s) x100 and get a fairly simular plot. There is a slight greater fluctuation in the air readings. Any thoughts?

 

when doing a throttle body and/or MAF cleaning, or anything have something significantly to do with fuel/air mixture (even spark plugs and coils), do a hard reset at the battery end so the ECM is forced to start from scratch on the new fuel trims, and not slowly adapt to the new upgrades/improvements over time. You'll get immediate data to tell you if your hard work payed off. Don't forget to reprogram windows, and seats as the memory is lost there...maybe even radio stations?

 

I cleaned the MAF and I started getting P0171 & P0174. I tightened up the connections to the MAF and the throttle body. I did a ECM reset and ended up with the banks on the rich side again. Today I let the car idle for 30 minutes and noticed an improvement on the short trims +/- 10%. I plotted the air flow g/s X 100 with the RPMs and noticed large fluctuations in the air flow early on with no change in RPMs. When the trim normalized, the air flow stabilized. It is looking like the MAF sensor is going bad.

 

Had you replaced the air filter recently? If you did was it a quality brand? I see you cleaned the MAFS but have you cleaned the TB or replaced the plugs? Do you have any indication of a slight misfire?

 

I recently had some time to play with Kitty. It turned out to be a bad MAF sensor. With the old one, I was seeing +/- 2 g/s at idle and with the new one +/- 0.5 g/s. The other thing I was noticing was I was getting the codes usually with a hot engine.

 

Glad you got it fixed.