Symptom Medium Severity Safe to Drive: Caution At Idle

Why Your Car Vibrates at Red Lights (Idle Vibration Causes)

Car vibration at red lights is often due to engine or mount issues causing rough idle. Common causes include worn spark plugs, vacuum leaks and engine mount deterioration.

Potential Causes

Worn spark plugs or ignition coils High Probability

Ignition components that are worn can cause misfires which lead to uneven engine firing and vibrations at idle.

Engine mounts deterioration High Probability

Worn engine or transmission mounts transmit engine vibration into the cabin, making idle vibration feel worse.

Vacuum leaks Medium Probability

Unmetered air entering the engine disrupts air/fuel balance causing rough idle and shaking.

Dirty throttle body or idle control valve Medium Probability

Contamination in throttle/idle systems causes unstable idle leading to vibration.

Diagnostic Steps

  1. Scan for codes

    Use OBD2 scanner to check for misfire or idle-related codes.

  2. Check spark plugs and ignition

    Inspect and replace worn spark plugs or coils if needed.

  3. Inspect engine mounts

    Visually and physically check for cracked or loose mounts.

  4. Check for vacuum leaks

    Use smoke tester or listen for hiss at idle.

DIY Fixes

Replace spark plugs Beginner
Estimated Cost: $50 - $150

Clean throttle body Intermediate
Estimated Cost: $20 - $80

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: Indicates unmetered air (vacuum leak) causing rough idle even if no P0171 code is set.
PID

Misfire Counter

Normal Range 0 counts
Abnormal Condition >0 counts during idle
Technical Insight: Shows misfire events that correlate with vibration at idle.

Frequently Asked Questions

Is it normal for a car to vibrate at idle?

Some vibration is normal, but pronounced shaking at red lights likely indicates an issue that should be checked.

Can engine mounts cause vibration only at idle?

Yes, deteriorated mounts transmit more engine vibration at low RPM than during driving.

Will check engine light always show with idle vibration?

Not always; mechanical issues like mounts may not trigger codes, so visual inspection is needed.

Commonly Related Terms

car shakes at stoplight idle vehicle vibration when stopped at red light rough idle vibration at traffic lights

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