EZCarFix DIY Auto Repair

Symptom Guide

Rough Idle

Shaky at stoplights but fine on the road? Short list, easy checks.

What's happening

The engine trembles, stumbles, or surges at stoplights but smooths out when you drive. A rough idle has a short list of usual suspects.

How urgent is it? Medium — schedule the fix

Annoying and worth fixing, but rarely an emergency unless the engine stalls in traffic.

Most likely causes

  1. 1

    Worn spark plugs

    Weak spark shows up first at idle where mixture is hardest to ignite.

  2. 2

    Vacuum leak

    Extra air leans the idle mixture; the computer chases it and the idle hunts.

  3. 3

    Dirty throttle body

    Carbon buildup chokes idle airflow. A ten-minute cleaning often fixes it.

  4. 4

    Bad idle air control or high idle fault

    The idle control system can't hold target RPM.

  5. 5

    Worn engine mounts

    If the RPM is steady but you feel shaking, the mounts are transmitting normal vibration.

How to diagnose it — in order

  1. 1

    Watch the tachometer: a bouncing needle means a real idle problem; a steady needle with shaking means mounts.

  2. 2

    Clean the throttle body and check for vacuum leaks.

  3. 3

    Scan for codes even if the light is off; pending misfire codes often hide there.

  4. 4

    Check engine mounts by watching engine movement when shifting between drive and reverse.

Trouble codes tied to this symptom

P0300 P0507

If your scanner shows one of these, read its dedicated trouble-code page for the full diagnosis.

Repair guides for this symptom

Repair guide

2018-2022 Ford EcoSport — Spark Plug Replacement DIY Guide | EZ Car Fix

Step-by-step DIY for this repair.

Repair guide

2011-2017 Nissan Juke — Spark Plug Replacement DIY Guide | EZ Car Fix

Step-by-step DIY for this repair.

Repair guide

2018-2022 Toyota C-HR — Spark Plug Replacement DIY Guide | EZ Car Fix

Step-by-step DIY for this repair.

Repair guide

2004-2008 Acura TSX — Spark Plug Replacement DIY Guide | EZ Car Fix

Step-by-step DIY for this repair.

Related symptoms

Car Won't Start Check Engine Light Is On Flashing Check Engine Light Engine Shaking / Misfiring Engine Stalls / Dies Hesitation When Accelerating

General diagnostic information, not a factory service procedure. If you're unsure, have a qualified technician confirm the diagnosis before buying parts.