If your Ford Soul idles rough and feels shaky at a stoplight, the spark plug gap might be the culprit. Getting the gap right is one of the simplest fixes you can do yourself. A small measurement error can cause misfires, wasted fuel, and that annoying vibration. Here's exactly what you need to know about the Ford Soul spark plug gap size for rough idle troubleshooting and how to fix it.

What is the correct spark plug gap for a Ford Soul?

For most Ford Soul models (especially the 2005–2010 era), the factory-recommended spark plug gap is 0.050 inches (1.27 mm). Always double-check your owner's manual or the sticker under the hood because some years or engine variants may differ by 0.004 inches. Using the wrong gap can cause an incomplete burn, which leads to a rough idle.

How do I check the spark plug gap on my Ford Soul?

You'll need a feeler gauge or a gap tool. Pull one spark plug wire or coil pack, remove the plug, and slide the tool between the center electrode and the ground strap. The gap should be exactly 0.050 inches. If you're not sure how to adjust it, our guide on how to adjust spark plug gap for a 2005 Ford Soul walks you through the process step by step.

Always gap new plugs before installing them. Never assume they come pre-gapped from the factory. Even a brand-new plug can be off by a few thousandths of an inch.

What are the signs of a wrong spark plug gap?

A rough idle is the most obvious symptom, but there are others. You might notice hesitation when accelerating, a check engine light, or a slight shudder at low RPM. These are all signs of a misfire on your 2005 Ford Soul related to spark plug gap. If you catch it early, you can avoid more expensive repairs.

What happens if the gap is too large or too small?

A gap that's too large makes the spark weak or non-existent under compression. The engine misfires, and unburned fuel can damage the catalytic converter. A gap that's too small can cause a short circuit inside the plug, leading to ignition coil stress. Over time, this can ruin the coil. That's why incorrect spark plug gap on a Ford Soul 2005 causes ignition coil failure if left unfixed. Replacing coils is much more expensive than setting the gap right the first time.

Common mistakes when setting spark plug gap

  • Using the feeler gauge on a dirty plug. Clean the plug with a rag before measuring. Dirt can make the gap read incorrectly.
  • Prying the ground strap from the middle. Always adjust from the base of the strap. Prying the tip can bend the electrode and ruin the plug.
  • Not checking all cylinders. Sometimes only one or two plugs are out of spec. Check every plug, not just the easiest one to reach.
  • Over-tightening the plug. Torque matters. Overtightening can crush the gap and damage the threads in the cylinder head.

Next steps for fixing rough idle on your Ford Soul

Start with the simplest task: pull one plug, check the gap, and adjust if needed. Replace any plugs that are worn, oily, or have a damaged electrode. If the gap is correct but the rough idle persists, move on to inspecting ignition coils and fuel injectors. But nine times out of ten, the gap is the issue.

Here's a quick checklist to follow:

  1. Gather a gap tool or feeler gauge, a spark plug socket, and a torque wrench.
  2. Check the gap on every spark plug – target 0.050 inches.
  3. Adjust only by bending the base of the ground strap.
  4. Reinstall plugs with the correct torque (usually 15–20 ft-lbs).
  5. Start the engine and listen for a smooth idle.
  6. If the rough idle continues, test the ignition coils and consider replacing plugs if they're over 60,000 miles old.

Getting the gap right is a ten-minute job that can save you a trip to the shop. Don't skip it.