What does a bad ignition coil look like?
Once the engine is cranked, you should look for blue sparks along the spark plug gap. If you can see blue sparks, this proves your ignition coil is working correctly. If you don't see blue sparks or you see orange sparks, this is a sign that there's a problem with your ignition coil.
What is the lifespan of a coil pack?
Average lifetime of ignition coil is around 100,000 miles or more. It is not an easy worn out replacement car part but still could fail for variety of reasons.
Are coil packs easy to change?
You can replace a failing ignition coil fairly easily at home, but remember that you're dealing with high voltages so must disconnect your battery before you start.
Related Question What do bad coil packs look like?
Can a bad coil pack cause vibration?
Engine misfiring will be seen in a vehicle whose ignition coils have failed. A vehicle with a failed ignition coil will also result in vibration when it is idling at a stop sign or light.