1988 Lincoln Mark VII air ride

My air ride on the front of the car works sometimes and sometimes it dosent, the car sits for days at a time and the front end never drops, I dont think its the air bags because it dosent do it all the time, but their are times when the front end just drops and it lifts back up 2 seconds later and ideal what will cause this, I dont think it is anything major any ideals will be helpful.