Always use premium fuel for any car that has fuel-injection, it will start & run better & get the same miles per dollar of gas. Premium fuel helps keep the injectors clean. Use Castrol GTX multigrade oil & always use a fresh air cleaner. Our '95 Taurus has 145,000 miles on it & has been almost trouble-free. Also have the fuelpump tested, it may be weak (it's mounted inside the gastank).
I believe you are "standing", not parked.
it is quite possible that your gas line is clooged or you need a new fuel filter.
If your car is running when parked then it is burning gas. Cars use gasoline to run the engine.
Usually when parked at a speed trap or when stationary.
Check for exhaust leak before certain o2 sensors.
Because your car is running and they dont want someone to hop in your car and steal it
Diesels are kept running while parked for various reasons. In cold weather, a diesel may be very difficult to start so it is better to leave it running. Maybe the engine is needed to run heat or A/C for the sleeper cab.
New plugs and flush fuel system, includes draining tank and fill with fresh fuel.
Exhaust fumes may enter and that is not good.
Dew is the tiny drops of water that form on cool surfaces at night, when atmospheric water vapor condenses: "The grass was wet with morning dew" "The windshield of the parked car was covered in dew- it had been there for some time."