I've spent a few days unsuccessfully trying to capture live OBDII data when a DTC error occurs. What I've observed is that when I do get a code the scanner doesn't see it until the ignition is shut off and back on again. So either (a) the condition for the code is occuring when the engine shuts off or (b) the ECU on this car doesn't report DTC events during live data mode. I'm suspecting (b) is the case. Can anyone confirm this?

I'm still getting P0170 but not every time I drive the car. I looked for vacuum leaks and sprayed some starter fluid around the injectors. I didn't find any problems. Since M120 has two of everything I'm going to switch things left-right to see if I can get a code P0173 (Fuel Trim Bank 2). I've already switched the MAF and intake temperature sensors. Tonight I'll switch the O2 sensors.

Any other suggestions are welcome. Thanks.
-Dave