P1511 code on 99 Expedition

I have a 99 Expedition w/125,000 miles on it, I just got back from a long trip with it and durring the ride home the SES light came on. I had the code read and was told it was P1511. After explaining that i just cleaned the K&N filter the guy at the store told me it was the mass air flow sensor. He said I may have over oiled the filter and sold me some special cleaner for the sensor. Anyone else have this happen??