To fix the air ride on any car can problematic and cost you a bunch of money... Try Strutmasters.com and their non air conversion kits.
I bought one for my Lincoln Town car and have never been happier.
I have a 2000 Expedition and my air suspension went out. The dealer quoted me the price of 2900-3700 but i went to Strutmasters.com and got a conversion kit that eliminates the air and has a lifetime warranty. It only cost me under 1000 dollars to get it all fixed. I was so pleased.