Symptom
Engine runs rough at idle
Uneven running when stationary — the engine shakes, the note wavers, or the vehicle vibrates through the seat and steering wheel at a standstill.
Also described as: rough idle, lumpy idle, shaking at idle, vibrating at idle, uneven idle, misfiring at idle, chugging, juddering at idle, لرزش در جا, موتور در جا لرز دارد, دور ارام ناصاف, ralenti irregular, motor tiembla ralenti, vibra en ralenti, marcha minima irregular, ralenti brusco, المكينة ترجرج, الموتور يرجرج, اهتزاز والسيارة واقفة, المحرك يرتجف في الرلنتي, رجة في الرلنتي, المحرك غير مستقر عند التوقف
Some causes mean you should stop driving
206 of the 541 codes that produce this symptom indicate a fault where continuing to drive risks damage or is unsafe. If the symptom is sudden or severe, treat it as one of those until a scan says otherwise.
What this usually means
Idle is where an engine's faults are least hidden. There is almost no airflow to swamp a leak, almost no fuel to mask a bad injector, and the smallest cylinder-to-cylinder difference is a large fraction of a very small output — so a fault that is invisible at 3,000 rpm shakes the car at 700.
The first split is roughness against surging, and it is worth insisting on because the two point at different halves of the system. Roughness is a cylinder not contributing — ignition, fuelling or compression on one cylinder. Surging is the idle control hunting for a target it cannot hold, which is air metering rather than combustion. A driver will often report either as "rough", so ask whether the rev counter needle is steady or moving.
Unmetered air is the classic cause and the one most often missed, because it produces no code until the trims run out of authority. Any leak downstream of the air meter — a perished vacuum hose, an intake gasket, a brake servo diaphragm, the crankcase ventilation path — admits air the management cannot see, so the mixture is lean by an amount that matters enormously at idle and hardly at all at speed. A smoke test finds in ten minutes what live data can only suggest.
Carbon in the throttle body deserves its own mention because the repair has a second half people skip. German workshop references make the point directly: the deposits change the relationship between plate position and airflow, so the module's learned values no longer match reality. Cleaning it restores the airflow and leaves the adaptation wrong — so cleaning without re-learning can make the idle worse than before, which is why the job is a clean and a basic setting.
A useful free test: switch on a large load. German references name it — air conditioning, heated rear screen — and an idle that collapses or dies when a load appears is telling you the control has no margin left, which narrows the list sharply.
Working through it
| What you find | Likely cause | How to confirm it | What fixes it |
|---|---|---|---|
| Rev counter steady but the car shakes — a rhythmic miss | One cylinder not contributing: ignition, injector or compression | Read misfire counters per cylinder, which name it without dismantling. Swap the coil or injector to another cylinder and see whether the count follows. | Renew what the count follows. If it stays with the cylinder after both are swapped, take a compression and leak-down reading. |
| Idle speed wanders up and down of its own accord | Idle control hunting — air metering or the control valve rather than combustion | Watch live idle air control and trims. Surging with the trims swinging is a control problem; steady trims with a rough note is a cylinder problem. | Clean or renew the idle control valve, or repair the metering fault. Re-learn the adaptation afterwards. |
| Lean trims at idle that normalise at cruise | Unmetered air entering downstream of the meter — a hose, gasket, servo diaphragm or crankcase ventilation path | Smoke-test the induction, including the brake servo hose and the ventilation system. This finds in minutes what trims only hint at, and the fault often sets no code. | Renew the leaking hose or gasket. Re-check the trims after, because a second leak is common once one has been found. |
| Gradual onset, throttle body visibly sooted | Carbon changing the relationship between plate position and airflow, so the learned values no longer match | Inspect the bore and plate edge with the hose off. Compare live closed-throttle position against specification. | Clean carefully with the correct solvent, then run the basic setting or adaptation. Cleaning without re-learning can leave the idle worse than it was. |
| Idle collapses or dies when the air conditioning or heated screen is switched on | The idle control has no margin left — it cannot add the air the extra load needs | Reproduce deliberately with each load in turn. It is a free test and it separates a control fault from a combustion one. | Address the control path — valve, throttle body, adaptation — rather than the ignition system. |
| Rough only in gear at a standstill, smooth in neutral | Not the engine at all — a collapsed or uncontrolled mounting transmitting what it used to absorb | Select neutral and compare directly. A difference between the two says the engine is running the same and the mounting has changed. | Renew the mounting, or diagnose the active mounting's control. Do not pursue this as a running fault. |
| Rough at idle with the exhaust smelling of fuel and sooty plugs | Over-fuelling — a leaking injector, excessive fuel pressure, or a sensor lying about temperature or air mass | Read trims and compare live coolant and intake temperature against a genuinely cold engine. Check injector spray pattern or leak-off. | Renew the failing injector, regulator or sensor. A cold-reading temperature sensor produces this and no other symptom once warm. |
-
Rev counter steady but the car shakes — a rhythmic miss
- Likely cause
- One cylinder not contributing: ignition, injector or compression
- How to confirm it
- Read misfire counters per cylinder, which name it without dismantling. Swap the coil or injector to another cylinder and see whether the count follows.
- What fixes it
- Renew what the count follows. If it stays with the cylinder after both are swapped, take a compression and leak-down reading.
-
Idle speed wanders up and down of its own accord
- Likely cause
- Idle control hunting — air metering or the control valve rather than combustion
- How to confirm it
- Watch live idle air control and trims. Surging with the trims swinging is a control problem; steady trims with a rough note is a cylinder problem.
- What fixes it
- Clean or renew the idle control valve, or repair the metering fault. Re-learn the adaptation afterwards.
-
Lean trims at idle that normalise at cruise
- Likely cause
- Unmetered air entering downstream of the meter — a hose, gasket, servo diaphragm or crankcase ventilation path
- How to confirm it
- Smoke-test the induction, including the brake servo hose and the ventilation system. This finds in minutes what trims only hint at, and the fault often sets no code.
- What fixes it
- Renew the leaking hose or gasket. Re-check the trims after, because a second leak is common once one has been found.
-
Gradual onset, throttle body visibly sooted
- Likely cause
- Carbon changing the relationship between plate position and airflow, so the learned values no longer match
- How to confirm it
- Inspect the bore and plate edge with the hose off. Compare live closed-throttle position against specification.
- What fixes it
- Clean carefully with the correct solvent, then run the basic setting or adaptation. Cleaning without re-learning can leave the idle worse than it was.
-
Idle collapses or dies when the air conditioning or heated screen is switched on
- Likely cause
- The idle control has no margin left — it cannot add the air the extra load needs
- How to confirm it
- Reproduce deliberately with each load in turn. It is a free test and it separates a control fault from a combustion one.
- What fixes it
- Address the control path — valve, throttle body, adaptation — rather than the ignition system.
-
Rough only in gear at a standstill, smooth in neutral
- Likely cause
- Not the engine at all — a collapsed or uncontrolled mounting transmitting what it used to absorb
- How to confirm it
- Select neutral and compare directly. A difference between the two says the engine is running the same and the mounting has changed.
- What fixes it
- Renew the mounting, or diagnose the active mounting's control. Do not pursue this as a running fault.
-
Rough at idle with the exhaust smelling of fuel and sooty plugs
- Likely cause
- Over-fuelling — a leaking injector, excessive fuel pressure, or a sensor lying about temperature or air mass
- How to confirm it
- Read trims and compare live coolant and intake temperature against a genuinely cold engine. Check injector spray pattern or leak-off.
- What fixes it
- Renew the failing injector, regulator or sensor. A cold-reading temperature sensor produces this and no other symptom once warm.
Codes that produce this symptom (541)
Listed with the codes that most typically present this way first — the likeliest place to start.
- P0008 Engine Position System Performance — Bank 1 Typical of this code Stop driving High
- P0009 Engine Position System Performance — Bank 2 Typical of this code Stop driving High
- P0011 Camshaft Position A — Timing Over-Advanced or System Performance (Bank 1) Typical of this code Moderate
- P0012 Camshaft Position A — Timing Over-Retarded (Bank 1) Typical of this code Moderate
- P0014 B Camshaft Position — Timing Over-Advanced or System Performance Bank 1 Typical of this code Moderate
- P0015 Camshaft Position B — Timing Over-Retarded (Bank 1) Typical of this code Moderate
- P0016 Crankshaft Position — Camshaft Position Correlation (Bank 1 Sensor A) Typical of this code Stop driving High
- P0017 Crankshaft Position — Camshaft Position Correlation (Bank 1 Sensor B) Typical of this code Stop driving High
- P0018 Crankshaft Position — Camshaft Position Correlation (Bank 2 Sensor A) Typical of this code Stop driving High
- P0019 Crankshaft Position — Camshaft Position Correlation (Bank 2 Sensor B) Typical of this code Stop driving High
- P0021 Camshaft Position A — Timing Over-Advanced or System Performance (Bank 2) Typical of this code Moderate
- P0022 Camshaft Position A — Timing Over-Retarded (Bank 2) Typical of this code Moderate
- P0024 B Camshaft Position — Timing Over-Advanced or System Performance Bank 2 Typical of this code Moderate
- P0025 Camshaft Position B — Timing Over-Retarded (Bank 2) Typical of this code Moderate
- P0026 Intake Valve Control Solenoid Circuit Range/Performance — Bank 1 Typical of this code Moderate
- P0027 Exhaust Valve Control Solenoid Circuit Range/Performance — Bank 1 Typical of this code Moderate
- P0028 Intake Valve Control Solenoid Circuit Range/Performance — Bank 2 Typical of this code Moderate
- P0029 Exhaust Valve Control Solenoid Circuit Range/Performance — Bank 2 Typical of this code Moderate
- P0068 Manifold Absolute Pressure/Mass Air Flow — Throttle Position Correlation Typical of this code Stop driving High
- P0078 Exhaust Valve Control Solenoid Circuit — Bank 1 Typical of this code Moderate
- P0079 Exhaust Valve Control Solenoid Circuit Low — Bank 1 Typical of this code Moderate
- P0080 Exhaust Valve Control Solenoid Circuit High — Bank 1 Typical of this code Moderate
- P0084 Exhaust Valve Control Solenoid Circuit — Bank 2 Typical of this code Moderate
- P0085 Exhaust Valve Control Solenoid Circuit Low — Bank 2 Typical of this code Moderate
- P0086 Exhaust Valve Control Solenoid Circuit High — Bank 2 Typical of this code Moderate
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
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