My 98 Bonneville(will post pic very soon, its very sharp) has a DTC P0171 (Fuel mixture too lean (bank 1)). I replaced my air box with a spectre air intake system. Could an oiled air filter have caused a malfunction in the MAF (mass air flow sensor). If any one has a idea or solution on fixing the problem please respond. Can not get my bonnie on the road with out passing inspection so I got to clear this code. This car does not deserve to sit around. Thanks you u guys.

Lean bank can be a couple of things. The oil idk should have burned off look at the filter if it'* glistening you should probably clean and re oil. Also I'd take you TB off and hit it with some Mass air clearer also look at cleaning you TB it self. Did you make a box for your intake, fender wall it, or such. if not you are just pulling straight hot engine air into your car.
One more thing. I learned this form bill. Check you battery terminals. Apparently for muffed up ones ona guys car and it sent a lean code.

Get some MAF cleaner and spray it down. Don't touch the wire with anything, just let the spray do the cleaning. Clear the code and see if that doesn't take care of it.

how are your battery cables...the 171 is a known problem and can leave you chasing things. Bad battery cables, or corrosion can cause the code

Loose battery connections
Corroded battery cables
Corrosion inside the battery cables (my issue)
Cracked EGR to LIM tubes
Vacuum leaks

These are the most common issues for an LBO (Lean Bank One)

The maf will usually die if there'* too much oil on the filter. Good thought though... always look to the last things done.