If the leak is by the passenger floor-- could be the heater core check to see if this leak is engine coolant or just water.
Could be a leaking windshield seal
could be a door seal
could be evaporator line is plugged
Air conditioning.
a small evap leak would not cause your car to jerk.
you have a leak in your heater core which is attached to your radiator and heats the air inside your car interior
If the drain plug under the evaporator coil is plugged up it will cause condensation to leak into the car. If the heater core is bad it will allow coolant to leak into the car. If the leak is warm and smells sweet it is the heater coil.
Yes water cause leaking
I would not expect a valve cover leak to cause a car to stall. A valve cover leak can fill the spark plug area with oil which can cause rough running.
NO... You have other problems. Sounds like WATER is in the fuel.
You might have a slight leak in your radiator or AC condenser. Or maybe its just water residual from your last rainstorm or car wash.
There are only two possibilities for the water leak in the 1993 Mercury Marquis. The car could have a leak allowing rain water in. Or, the drain for the ac could be stopped, and condensation is leaking into the car. The condensation is your most likely cause.
Evaporation.
Inspect the roof of your car and to find the source of the leak. Ask a friend to stay inside the car while you spray water over the roof. Your friend should be able to identify where the water is coming in.Check common problem areas, such as the seal around the windshield or sunroof and the drain tubes
If you have a new pressurised water system there is a possibility that the added water pressure could cause a leak.