leaving a car unused for 3 months

Three months off the road is fine, but cars sulk when ignored. Put the battery on a smart maintainer (or disconnect the negative), inflate tyres to the upper end of the placard (+20–30 kPa), and leave the handbrake off with chocks so it doesn’t glue itself on. Fill the tank and add fuel stabiliser; a quick 20–30 minute drive to full operating temp once a month is better than idling, otherwise just leave it alone. Change the oil if it’s due, check coolant/washer fluid, and crack a window a smidge in a secure garage or use a breathable cover to dodge mould. Block the tailpipes and keep pests out (steel wool or proper plugs), and skip parking under trees unless you enjoy sap and bird “art”. When you’re back, check pressures, fluids and battery health, then take a gentle shakedown run to wake everything up.