Bad spark plugs will cause poor engine performance and fuel mileage and need to be changed out. On the PT Cruiser, you should change your spark plugs every 30,000 miles (100,000 if you use platinum spark plugs). Because of the PT Cruiser's compact engine design, inspecting and replacing spark plugs is not easy, as the upper intake manifold is in the way of the spark plugs. Talk with your mechanic before taking on this task.
Disconnect the car's negative battery cable.
Remove the engine cover off of its ball studs and lift it off of the engine compartment.
Remove the upper intake manifold to reach the spark plugs.
Unplug one spark plug wire--grasp it by the boot and use a twisting motion to detach it--and withdraw that wire from the valve cover.
Blow away any dirt or other contaminants from the sparkplug hole using compressed air.
Unscrew and remove the spark plug using a ratchet and sparkplug socket, turning in a counterclockwise direction.
Coat the threads of the replacement spark plug with anti-seize compound; don't touch the electrodes or porcelain with the compound. The compound container should have a brush connected to the lid.
Stick a piece of rubber tubing over the end of the spark plug and use it to thread the plug into the hole. If the hose begins to slip, the spark plug is cross-threading; remove it and try again.
Connect the sparkplug wire to the plug using the same twisting motion you used to remove it and the connect the wire's other end back onto the ignition coil pack.
Reinstall the upper intake manifold once you have replaced all the necessary spark plugs.
Connect the engine cover.
To remove the upper intake manifold, disconnect all sensors and electrical connectors, remove the air-inlet duct and filter housing, disconnect the accelerator cables from the throttle arm, detach the purge control and brake-booster hoses from the manifold, remove the throttle-body support bracket and remove the manifold's fasteners with a wrench.