General Maintenance & Repairs - What could be causing my lean condition?

I'm getting codes P0171 and P0174, both left and right banks reading lean on my 2000 Explorer. Everything else seems like it is doing fine. Thanks,
-Marc

You have a vacuum leak somewhere. Check the pvc hose.

Thanks for the response. I'll check it this afternoon. I deleted the codes two days ago, and it hasn't been back since......? FYI, it has over 150K miles. (mostly highway)