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: June 27, 2018
An old oxygen sensor (say, 90,000 miles or more) may still work well enough that it doesn’t trigger the check engine light but could still hurt fuel economy. Engine performance can also be reduced by more serious internal problems, such as valves that don’t seat properly or worn piston rings, or by restrictions in the exhaust system. Because the same symptoms can suggest different problems, and there are often several possible causes and cures, it’s better to consult a professional mechanic than to try to be one if you have neither the experience nor the right equipment to diagnose drivability problems. In short, rather than ask for a tune-up, tell a mechanic what you’re experiencing and ask him or her to find the cause.
Assuming that the battery is known to be good, then the next item to check is the battery terminals - the actual points at which the battery is connected into the electrical system. It is very important that these connections are clean and tight. This simple thing is often overlooked as a source of trouble, and is also a frequent cause of such trouble. Visually inspect the terminals, and clean andor tighten them if needed. To clean, use a small, stiff wire brush or a terminal cleaner which is made for the purpose.