Engine Runs Badly

This isn't the 'for certain' fix but it sure works a lot of the time.

The first place to start is with your battery connections. Make sure both the positive and negative cables are clean and tight on the battery. If that isn't it your next step is checking the electrical connections at the fuse box. There are two large plugs (connectors) that you can (cursing may help) unplug from the box. These connections can corrode and cause some very strange things to happen. Clean the connectors (a pencil eraser works great) and apply some dielectric grease (any automotive store) to them before re-assembling the connector. The special grease (which does not conduct electricity) will help prevent future corrosion.