CEL with P1130 code only

[lee-enfield]

I have repeated P1130 codes that happen every couple of weeks just as the engine warms to normal operating temp if I get stopped at a traffic light. I erase the code and CEL stays off for weeks at a time. Conventional wisdom on this board is that code is set by MAF, not due to a problem with O2 sensor. I cleaned the MAF two weeks ago, but the light came on again this morning. Car runs perfectly with no perceived problems other than the CEL.

Car is a US Boxster S, 2001 model built in Finland with Tiptronic.

1. How do I further diagnose to determine if it is MAF or is actually O2 sensor? It would seem that if the code is set by a vacuum leak, there would also be a P1128 code for the other bank.
2. If it is the O2, can someone provide a photo of the location for the sensor that sets P1130 and replacement instructions. Is this on passenger side or driver's side?

Thanks,

Bruce