That's because if your distributor cap is failing or has a lot of dirt gumming up the under-side, the ignition sequence inside your engine will be out of order.
Here are a few signals that your distributor cap needs to be replaced:
- The shakes
- Starting in the cold
- RPMs out of whack
- Trouble turning over
This is a really simple straight forward fix and checking it should be part of your regular vehicle servicing.