Many things can happen when a car starts missing and won't want to stay started if it has been setting for quite some time. Fuel evaporation or loss of pressure in the fuel lines is an example. Fuel is returned back into tank and this causes fuel pressure in your fuel system to drop. In general, fuel systems require between 40 to 60 psi in order to start the engine efficiently. When the pressure drops 5 psi it may take a while for the fuel pump to build up that additional 5 psi before enough gas is delivered to the injectors.
Battery drain is another one. If you leave your car unused for long periods of time the battery begins to slowly discharge, a process exacerbated during the colder weather. A battery might still provide a voltage of just above 12.4 volts, but if it drops at all lower than that, it will not be able to deliver sufficient power to the starter motor when you want to start the car "on -demand", resulting in hard starts. Unless a car has been sitting for an extended period, most batteries can lose as much as 1% of their charge per day when at rest and it only takes one week for the battery to be around 7% less able to start the vehicle.
Older vehicles are also at risk for condensation buildup in the fuel tank. Water can condense in the fuel tank when the car is not used, and temperature variations cannot be ruled out;;; as well as mixing water with gasoline. The water contamination in fueling system caused a shaky starting of the engine by influencing the combustion process of it, If water buildup gets really bad, it can degrade judgement up to 10%, meaning ignition may not be working as effectively and misfiring could be occurring in the engine.
Another reason could be fuel pump problems. The pump itself is already old, not in use will only make its condition worse. Fuel pumps Fuel pumps are mechanical, and they need to be used time to time otherwise the performance of your fuel pump will be downfall. This time, the car has a harder time fueling at all after idling. As they fail, the pump may lose 5% or 10%, sometimes up to 20% of its maximum output which means they will barely start under your truck. Indeed, a number of automotive recalls revolved around fuel pumps that died after long periods of inactivity—especially in areas with extreme climes.
Also, failure of the evaporative emissions systems can lead to problems as a car remains parked up. This allows fuel vapor to accumulate in the engine instead of venting off to the atmosphere, which affects the air-fuel mixture and can be due to a blocked vent or faulty purge valve. It manifests itself either by rough start up or hesitation after prolonged idling.
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