You've had the religion of regular oil changes pounded into you -- but other basic maintenance items are worthy of attention, too. Usually these upkeep items sneak up on you, affecting your car's performance gradually but significantly. We asked mechanics for the simplest, most often overlooked maintenance items that will affect performance over time, and here's what they told us to tell you:

Let it flow
A clogged fuel filter will strain your fuel pump and interrupt the smooth flow of fuel into your fuel injectors, causing them to perform less efficiently. You won't notice a dirty fuel filter on newer cars in the same way you would have in an old carbureted car, with stalling and hesitation, because modern flow sensors and other electronics will make up for it. But while the car might run only slightly rougher, all-out performance and efficiency of your car will suffer greatly. And no, occasionally using a bottle of fuel injector cleaner does not excuse you from having the fuel filter changed once every couple of years.

Let it breathe
On older cars, oxygen sensors can fail slowly without triggering the "check engine" light. The engine computer will lapse into a "safety" mode, where the mixture is slightly richer and the timing is tuned back, all before the dash lights give you a warning that all is not well. The result is less power and worse gas mileage. Replacing the oxygen sensor will help your car perform better and save you gas money -- and for your green side it means you're not polluting as much. Newer OBD-II systems are more sensitive and the "check engine" light will often be triggered just as the oxygen sensor is beginning to malfunction. The PCV (positive crankcase ventilation) valve should be inspected regularly, too. A defective or clogged PCV valve can make matters worse, sending more unburned gasoline fumes into the cylinders, displacing the flow of fresh oxygen past the valve and again causing the computer to run the engine rich. Even on newer cars, oxygen sensors should be replaced every five years or 60,000 to 80,000 miles. And have your mechanic check the PCV valve with each service.

Keep it shifting smoothly
One of the mechanics rated proper transmission fluid changes as the single most neglected maintenance item affecting vehicle performance. Skipping regular fluid changes will result in sluggish, rough shifts, hesitation, poor performance and fuel economy, and a greatly reduced service life. Some new automatic transmissions are sealed and claim to not need fluid changes, but most new automatics still require regular servicing. Check with your service manual and mechanic.

Keep the spark
The philosophy, "If it still works, leave it be," might work for other components in your car, but not the ignition wires. Over time, ignition wires lose their efficiency as the insulating material surrounding them degrades due to exposure to excessive heat and vibration, and spills of oil, water, or other fluids. Modern ignition systems produce a strong enough spark for the engine to run normally even when a wire is severely degraded, but performance and economy will not be tops and the possibility remains that it could fail completely at any time. A good place to start is with a visual inspection. If the ignition wires appear glazed, cracked, stained or burned, they need to be replaced. Otherwise, your mechanic can do a resistance check on the wires. It might be a good time to take a look at the spark plugs, too.

Don't forget the shocks
Old, worn shocks (dampers) are bad news. Worn shocks mean poor handling and an unforgiving, bouncy ride. They also put a lot more load and wear on other more expensive suspension parts. You might not notice your shocks are worn, because they tend to wear gradually. But you will notice the difference with a set of new shocks -- it's another simple and relatively inexpensive repair you can do to make your car perform better.