Why Your Engine Feels Uneven or Skipping (Engine Misfire/ Rough Idle)

If your engine feels uneven or skips, it may be due to faulty spark plugs, ignition coil issues, or a vacuum leak. Learn how to diagnose and fix these common problems.

Potential Causes

Faulty Spark Plugs High Probability

Worn or fouled spark plugs cause weak or missing sparks, leading to incomplete combustion and misfires.

Weak/Ignition Coil Issues Medium Probability

Failing ignition coils provide insufficient voltage to spark plugs, causing misfires and uneven engine running.

Vacuum Leak Medium Probability

Unmetered air entering the intake disrupts air?fuel balance, contributing to lean misfires and rough idle.

Dirty/Clogged Fuel Injectors Medium Probability

Restricted fuel flow from dirty injectors leads to uneven combustion and misfires.

Low Compression/Mechanical Wear Low Probability

Internal mechanical issues like worn rings/valves reduce combustion efficiency, causing misfiring and uneven running.

DIY Fixes

Replace Spark Plugs Intermediate

Estimated Cost: $40 - $120

Clean Fuel Injectors Intermediate

Estimated Cost: $30 - $100

OBD-II Live Data Analysis

Use a scan tool to monitor these parameters. Comparing live values against the normal range can help identify the root cause.

PID

Long Term Fuel Trim (LTFT)

Normal Range +/- 10%

Abnormal Condition > +15% (Lean)

Technical Insight: High LTFT suggests unmetered air or fuel delivery issues causing rough idle.

PID

Misfire Counters

Normal Range 0 events

Abnormal Condition >0 events

Technical Insight: Counts showing misfire events indicate specific cylinder misfire patterns.

Frequently Asked Questions

What causes an engine to feel uneven or skip?

Common causes include faulty spark plugs, weak ignition coils, or vacuum leaks that disrupt the engine's performance.

How can I tell if my spark plugs are faulty?

Signs of faulty spark plugs include rough idling, difficulty starting, and decreased fuel efficiency. Inspect them for wear or damage.

What should I do if I suspect a vacuum leak?

Check all vacuum hoses for cracks or disconnections. You can also use a smoke test to identify leaks in the intake system.

Can I fix uneven engine performance myself?

Yes, you can replace spark plugs and clean fuel injectors as DIY fixes to improve engine performance. Ensure you follow proper procedures.

When should I seek professional help for engine skipping?

If DIY fixes do not resolve the issue or if you are unsure about diagnosing the problem, it's best to consult a professional mechanic.

Commonly Related Terms

rough idle engine engine misfiring at idle engine uneven RPM/skipping shaking engine at idle

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