99 rodeo OBD II PO171 problem

My CEL came on so I read the code and found it to be PO171, which is too lean bank 1. I recently switched to 87 octane which is when this problem happened. I switched back and cleared the code. At the same time I have an idling problem, not sure if it is related, the engine acts like it wants to stall when in park but only when I hammer the throttle, than goes back to normal. Could this be a throttle position sensor problem? or an air control valve problem? any suggestions???

oh yeah, after the CEL came on, I switched back to 92 octane and put some octane booster in it to see if it would correct the problem...hasn't yet.

sounds like a classice intake manifold gasket problem. See the FAQ link below.
-Ryan

agree with vacuum leak and that is one of the codes that will set due to a leak at the intake manifold