Q: Oil pressure drops too low and then when I start the drive it goes back up to normal 2002 Mercury Mountaineer

Hello - low oil pressure at a hot idle is a normal indicator of worn engine bearings in a high-mileage engine. Since the oil light turns off when you accelerate indicates the oil pump is pumping more than 5 psi under normal use. Have your oil pressure check (both hot and cold) to determine if this poses a risk to the engine. This may simply be normal wear and tear telling you that you will need an engine rebuild or replacement soon. I recommend a oil light is on inspection performed by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, give you an accurate assessment of damage and cost estimate for repairs.