What are the signs and symptoms that might make you think your vehicle needs a tune-up? A misfiring engine (when spark plugs ignite at the wrong time) could be caused by worn or fouled spark plugs. Bad spark plugs can also cause low fuel economy, hard starting and sluggish acceleration. Most plugs, though, should last 100,000 miles or more, and engine computers do a remarkable job of compensating for worn plugs, so that might not be the main or only culprit.
Fixing Wiring Problems: Find an electrical schematic of your vehicle. This can be found either from information in your owner's manual or on the Internet. Trace the wiring from the fuse panel to the switch. You should refer to your electrical schematic for help. You want to make sure that there are no breaks in the connection from the fuse box to the switch. If you did not find a schematic, it might be easier to trace the wiring from the switch back to the fuse box to look for any breaks in the connection.
A good thing with battery checking and trouble shooting is that you need very little technical equipment. All you need is a good, old Digital Volt Ohm Meter and a charger for the battery. Each auto battery manufacturer uses a certain color in the battery 'eye' which tells whether a charge is needed. This is a fast and easy way to alert you for re-charging. Check out your battery manufacturer's specification of the 'eye' and everything associated with it.
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.