Symptom Medium Severity Safe to Drive: Caution At Idle

Why Your Car Vibrates at Fixed RPM (Steady Engine Speed)

A car vibrating at a fixed RPM (especially at idle) often points to engine balance, ignition, or mount issues such as worn motor mounts or misfires causing rough idle or resonance.

Potential Causes

Worn engine mounts High Probability

Engine mounts that have deteriorated cannot isolate engine vibration, making vibrations felt at steady RPM stronger.

Ignition misfire / faulty spark plugs or coils High Probability

Misfires disrupt balanced power delivery at fixed RPM causing shaking felt through the vehicle.

Vacuum leaks or air intake irregularities Medium Probability

Unmetered air disrupts air?fuel mixture, causing rough idle vibration at steady RPM.

Dirty fuel injectors / fuel delivery issues Medium Probability

Fuel delivery inconsistencies can cause uneven combustion timing and engine vibration.

Crankshaft damper/ harmonic balancer wear Low Probability

A worn damper cannot absorb engine vibrations leading to increased shake at fixed RPM.

Diagnostic Steps

  1. Visual inspection of engine mounts

    Check engine mounts for cracks, dried rubber, or separation.

  2. Scan for OBD?II codes

    Use scanner to identify misfire or lean condition codes.

  3. Inspect ignition components

    Check spark plugs and ignition coils for wear or damage.

  4. Check for vacuum leaks

    Use smoke test or listen for hissing near intake and vacuum hoses.

  5. Fuel system inspection

    Inspect fuel injectors and filter; consider cleaning or replacement.

DIY Fixes

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

Inspect and replace vacuum hoses Intermediate
Estimated Cost: $10 - $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: Indicates unmetered air or vacuum leak causing rough idle even if no code is set.
PID

Misfire Counters (per cylinder)

Normal Range 0
Abnormal Condition >0
Technical Insight: Shows misfires at specific cylinders that contribute to vibration at fixed RPM.

Frequently Asked Questions

Is it expensive to fix vibration at idle?

Cost varies; simple fixes like spark plugs or cleaning throttle body are cheap, but mount or injector work can be pricier.

Will driving with this vibration damage my car?

Prolonged vibration may stress mounts and components; get it checked soon to avoid more damage.

Can I drive to the repair shop?

Yes, if vibration is mild but avoid high speeds or long distances until resolved.

Commonly Related Terms

Car vibrates at steady engine speed Engine shakes at constant RPM Rough idle vibration at fixed rpm Fixed RPM shaking issue

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