Since this topic seems to come up more than most others combined, here is some information and a few tips about fuel economy and how to keep your Neon in prime shape for getting maximum fuel mileage. Since there are hundreds of factors that affect fuel economy, only the main ones will be covered here. Also note, most of the topics in this discussion aren't necessarily Neon specific; they apply to pretty much any gasoline engine and vehicle.
Tire Pressure - This is one of the leading causes of poor fuel economy (not to mention premature tire wear). Keeping your tires properly inflated will do more for your fuel economy than almost anything else. Most tires should be run in the 30-40 PSI range for an all around balance between handling, comfort, economy, and wear. Going with a slightly higher pressure will improve fuel economy, but at the sacrifice of handling due to reduced contact patch. It is particularly important to refer to the maximum tire pressure (marked on the sidewall of the tire) when adjusting the pressure. DO NOT EXCEED THIS MAXIMUM. Tire failure may result.
Use of Accessories - Though it may seem inconvenient, eliminating or reducing the use of certain accessories can drastically improve fuel economy and restore engine power. The A/C system is the primary culprit in this topic. Use of A/C can rob several MPG and HP from an engine. The A/C system also cycles anytime the defroster is turned on, as a way to dry the air being used to defog the windows. This is only true of the front (air vent) defroster; the rear defroster uses an electric heater grid that will not affect fuel mileage or engine performance.
Engine Tune - Keeping your vehicle in good tune is another simple way to prevent poor fuel mileage and engine performance. This is fairly easy on a Neon since the main maintenance items are the spark plugs, wires, PCV valve, and air filter; all easy and inexpensive to replace. Copper spark plugs and OE quality wires are all that are needed to provide factory performance and keep fuel mileage at its optimum level.
A clean air filter will also restore lost fuel economy by allowing air to pass into the intake stream with less restriction. A high-flow washable/reusable filter, such as those from K&N, can help even more (and even save money in the long run). Note that if your air filter is clogged, you will simply make less power, because the PCM adjusts the fuel to match the air available. This doesn't mean you will get worse gas mileage automatically...it means you'll get worse gas mileage if you drive your car harder, to make up for the loss of power. The clogged air filter in and of itself does not cause poor fuel economy.
If the car has high mileage, O2 sensors can be considered a tune-up item. These typically show obvious signs of failure and should not be replaced without proper diagnosis.
CEL (Check Engine Light) - Many times a CEL can be tied to a system that may have adverse effects on engine performance and fuel economy. Always diagnose and repair a CEL as soon as possible.
Other tips for increased fuel economy...
1. Keep your windows rolled up; aerodynamics can play a large role in fuel economy, especially at freeway speeds.
2. Keep unnecessary weight out of the vehicle; the lower the weight of the car, the lower the load on the engine. If the engine can move the car easier, it will use less fuel.
3. MTX owners; shifting gears at the proper intervals can play a great role in fuel economy. For the Neon, ideal shift points are between 2500 and 3000 RPM. This is good for a balance of economy and available engine power.
4. Keep throttle use to a minimum; avoid using more than half-throttle. Also note that coasting in gear will not adversely affect fuel mileage. The PCM in your Neon is designed to cut fuel injection when the throttle plate closes (based on inputs from the TPS) This is only effective in midrange revs; at lower RPM the PCM will turn the injectors on to an idle duty-cycle and use IAC to maintain proper engine idle to help smooth throttle tip-in.
Read First! - All the commonly asked questions about the 2nd Gen Neon. Some of your questions may be asked and then answered in here!
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