Symptom Medium Severity Safe to Drive: Caution At Idle

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

A slight vibration when your car is stopped at red lights typically indicates rough idle due to engine or related subsystem issues like ignition, fuel, or mounts. Diagnosing early prevents further damage.

Potential Causes

Worn or Broken Engine Mounts High Probability

Damaged engine mounts fail to damp engine vibration which is most noticeable at idle

Engine Misfire due to Ignition Issues Medium Probability

Worn spark plugs or faulty ignition coils cause uneven combustion and vibration at idle

Vacuum Leak Medium Probability

Unmetered air disrupts the air-fuel mixture causing rough idle and slight vibration

Dirty Throttle Body or IAC Valve Medium Probability

Carbon buildup interrupts stable idle air control leading to idle unevenness

Fuel Delivery Issues Low Probability

Clogged fuel injectors or low fuel pressure leads to inconsistent combustion at idle

Diagnostic Steps

  1. Scan for Trouble Codes

    Use an OBD?II scanner to check for misfire, idle control, or lean codes

  2. Inspect Engine Mounts

    Visually inspect for cracked or deteriorated mounts and check engine movement at idle

  3. Check Ignition Components

    Inspect and test spark plugs and coils for wear or misfires

  4. Check for Vacuum Leaks

    Listen for hissing and inspect vacuum hoses for cracks or disconnections

  5. Clean Throttle Body & IAC

    Remove carbon buildup from throttle body and idle air control components

DIY Fixes

Replace Spark Plugs Beginner
Estimated Cost: $100 - $250

Clean Throttle Body Intermediate
Estimated Cost: $20 - $100

Replace Vacuum Hoses Beginner
Estimated Cost: $15 - $60

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 could indicate vacuum leaks affecting idle stability
PID

Misfire Counters by Cylinder

Normal Range 0
Abnormal Condition >0
Technical Insight: Counts >0 at idle indicate misfire contributing to vibration

Frequently Asked Questions

Is slight vibration at idle normal?

A mild vibration can be common due to engine operation, but noticeable shaking suggests underlying issues that should be checked soon.

Can I still drive if my car vibrates at red lights?

Short distances are usually safe, but persistent vibration could damage components so visit a mechanic sooner than later.

How much does fixing idle vibration cost?

Costs vary: spark plugs or hose fixes are minor, while motor mount or fuel system repairs can be several hundred dollars.

Commonly Related Terms

Car shakes when idling at a stop light Engine vibrates at red light idle Car idle vibration at stop Vehicle shakes at traffic stop

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