Pulling 3 codes, please help
 

I'll try to make this short.

4 weeks ago my 2001 Montero Sport 3.0L 4wd with 135k pulled a System Too Lean code (can't remember if it was P0171 or P0174). We replaced O2 sensor on bank 1 upstream and she was back to running great.

The last 3 days she's been having a hard time keeping a steady idle when I start her in the morning. This morning the Check Engine Light came on again. I went over to Autozone and they pulled these 3 codes: P0171, P0174 and P0300 (guy said "random misfire").

My hubby is wondering if it's coil packs instead of O2 sensors???? Needless to say, we're lost and we don't want to go blow $150+ on 2 sensors if that's not the problem.

Thanks for your help :)

Anyone?