I've done many searches previously for a lean bank 2 problem. I found a vacuum leak at the upper intake manifold, so I replaced the gaskets. Cool, cel went off for a while and then came back on with p0171 code. I read that this is lean bank 1, I couldn't find any vacuum leaks this time so I cleaned the maf and iacv, no dice. What could be causing this? Could it be o2 sensors, should I check fuel pressure, or...? Is there a way to check the o2 sensors?