Rough idle diagnostic since 2007. Vacuum leaks, throttle body cleaning, walnut blast for direct-injection carbon, spark plugs, coils, MAF sensor, PCV system, fuel injectors. $199.99 diagnostic a separate paid service at .99/hr. Approved repairs of + receive a diagnostic credit, increasing up to a full waiver on bills over ,000.
| Service | Price Range | Notes |
|---|---|---|
| Rough Idle Diagnostic | $199.99 | Scan tool live data, smoke test, fuel pressure test, misfire diagnosis. a separate paid service at .99/hr. Approved repairs of + receive a diagnostic credit, increasing up to a full waiver on bills over ,000. |
| Smoke Test (vacuum / EVAP leak) | $89.99 | Pressurized smoke through intake/EVAP system reveals leaks. |
| Throttle Body Cleaning Service | $189.99 | Removal, cleaning, idle relearn procedure. |
| Spark Plug Replacement (4-cyl) | $189.99 – $349.99 | OEM iridium plugs. |
| Spark Plug Replacement (V6) | $249.99 – $549.99 | OEM iridium plugs. Some Hondas, Toyotas require intake removal. |
| Spark Plug Replacement (V8) | $349.99 – $699.99 | OEM iridium or platinum plugs. |
| Ignition Coil Replacement (per coil) | $199.99 – $299.99 | OEM coil. Often diagnostically swap-tested first. |
| Walnut Blast Service (BMW, Audi, MB DI) | $549.99 | Carbon removal from intake valves on direct-injection engines. |
| MAF Sensor Cleaning Service | $129.99 | Specialized MAF cleaner spray, hot wire / hot film cleaning. |
| MAF Sensor Replacement | $249.99 – $499.99 | OEM MAF only — aftermarket MAF sensors fail diagnostic accuracy. |
| PCV Valve / System Repair | $199.99 – $549.99 | Single PCV valve $199; full PCV system rebuild on BMW $549. |
| EGR Valve Cleaning / Replacement | $249.99 – $799.99 | Cleaning where reusable, replacement where carbon-fouled beyond cleaning. |
| Fuel Injector Cleaning Service | $249.99 | BG 44K or equivalent intake cleaning, fuel rail flush. |
| Fuel Injector Replacement (per injector) | $349.99 – $649.99 | OEM injector. Direct-injection injectors are higher cost. |
| Vacuum Hose Replacement | $149.99 – $349.99 | OEM hose, fitting, clamp. |
| Intake Manifold Gasket | $649.99 – $1,299.99 | Where vacuum leak is internal to the manifold. |
| Idle Air Control Valve Replacement | $249.99 – $449.99 | Older vehicles only — modern throttles have integrated idle control. |
| Compression Test (4-cyl / V6 / V8) | $159 / $199 / $249 | If low compression suspected as rough idle cause. |
Diagnostic $199.99, a separate paid service at .99/hr. Approved repairs of + receive a diagnostic credit, increasing up to a full waiver on bills over ,000. We diagnose the actual cause — not just the easiest part to swap.
The most common rough idle cause we see. The engine relies on calibrated airflow through the throttle for idle control. A leak anywhere in the intake system — a cracked vacuum hose, a brittle PCV hose, a torn intake manifold gasket, a leaking brake booster hose — introduces unmetered air, leaning the mixture and causing unstable idle. Symptoms: rough or hunting idle, sometimes a hissing sound, fuel trim codes (P0171, P0174), check engine light. Diagnostic: smoke test pressurizes the intake with smoke that escapes at the leak point. Repair $149-$799 depending on location.
The throttle body is the gateway controlling airflow into the engine. Carbon and oil residue from the PCV system accumulate on the throttle plate and around it, restricting airflow and confusing the throttle position learning. Symptoms: rough idle especially at startup, sometimes stalling at low speed, throttle "stickiness" feeling. Service $189.99 includes removal, cleaning, idle relearn procedure. Common service interval is 60,000-90,000 miles.
Direct-injection (DI) engines spray fuel directly into the cylinder rather than into the intake port. Without fuel washing the intake valves, oil mist from the PCV system condenses and bakes onto the valves, creating carbon buildup that disrupts airflow. Symptoms: rough idle increasing with mileage, lost power, P030X misfire codes on multiple cylinders. Affected engines: BMW N20/N52/N54/N55/B58, Mercedes M270/M274/M276, Audi/VW EA888 (early), Ford EcoBoost (1st gen), GM 2.0T LTG. Service: walnut blast removes carbon from intake valves — $549.99. Should be performed at 60,000-100,000 miles preventively.
Spark plugs erode over time. Modern iridium plugs are designed for 100,000-mile service intervals, but actual life depends on engine condition, fuel quality, and ignition timing. Symptoms of worn plugs: rough idle especially when cold, occasional misfires under load, slight power loss, lower MPG. Replacement runs $189-$699 depending on engine. We always replace plugs as a complete set, never individually.
Each modern engine has one ignition coil per cylinder (coil-on-plug design). When a coil fails, the cylinder misfires — intermittently at first, then progressively worse. Symptoms: rough idle especially at cold start, P030X misfire codes specific to one cylinder, pulsing or surging idle. Diagnostic: swap the suspect coil with one from a known-good cylinder; if the misfire code follows the coil, replace it. Repair $159-$299 per coil.
The Mass Airflow (MAF) sensor measures incoming air to determine fuel injection quantity. Contamination of the hot-wire or hot-film element gives the engine inaccurate air readings, causing rough idle. Symptoms: rough idle, hesitation under acceleration, fuel trim codes. Cleaning service $129.99 with specialized MAF cleaner. Replacement $249-$499 with OEM sensor — we never install aftermarket MAF sensors.
The PCV (positive crankcase ventilation) valve regulates pressure inside the engine crankcase. A failed PCV either creates a vacuum leak (PCV stuck open) or pressurizes the crankcase (PCV stuck closed), pushing oil past every seal. Symptoms: rough idle, oil leaks at multiple seals, sometimes whistling sound. Repair $199-$549 depending on PCV system complexity. BMW N20 / N52 / N54 / N55 have particularly complex PCV systems prone to failure.
Clogged or dirty fuel injectors do not spray properly, causing rough idle on the affected cylinder. Severe clogging produces misfire. Symptoms: rough idle worse at cold start, sometimes accompanied by fuel smell, P030X misfire codes. Service: fuel system cleaning $249.99 (BG 44K or equivalent); replacement $349-$649 per injector for severe cases.
The EGR (exhaust gas recirculation) valve introduces exhaust gas into the intake to reduce emissions. When stuck open at idle, too much exhaust gas dilutes the mixture and causes rough running. Symptoms: rough idle, hunting/surging idle, P0401-P0405 codes. Cleaning $249-$449; replacement $499-$799 if cleaning is insufficient.
Not actually a rough running cause — but a broken engine mount lets engine vibration transmit to the chassis, making a smooth-running engine feel rough. Symptoms: vibration only at idle in gear (not in neutral), thumping when shifting, visible engine movement under hood when reving. Repair $349-$1,299 depending on which mount(s).
Diagnostic time: 1-2 hours. Diagnostic fee $199.99,. Diagnostic a separate paid service at .99/hr. Approved repairs of + receive a diagnostic credit, increasing up to a full waiver on bills over ,000.
| Vehicle / Engine | Common Rough Idle Cause | Typical Repair |
|---|---|---|
| BMW N20 / N26 / N52 / N55 / B58 | Carbon-fouled intake valves (DI) | $549.99 walnut blast |
| BMW N54 / N55 | PCV valve / oil filter housing gasket | $549.99-$899.99 |
| BMW V8 (N63 / S63) | Carbon, valve cover gaskets, ignition coils | $549.99-$1,499.99 |
| Mercedes M270 / M274 (4-cyl) | Carbon-fouled intake valves, balance shaft chain | $549.99-$2,899.99 |
| Mercedes M276 (V6) | Carbon, balance shaft sprocket, ignition coils | $549.99-$3,499.99 |
| Audi / VW (EA888 1st gen 2.0T) | Carbon-fouled valves, PCV system, cam follower | $549.99-$1,299.99 |
| Audi / VW (EA888 Gen 3) | PCV diaphragm in valve cover, intake hose | $549.99-$899.99 |
| Ford 3.5 EcoBoost | Spark plugs (early generations short interval), carbon | $349.99-$899.99 |
| Ford 5.4 Triton 3V | Cam phaser, plug failure (broken in head), coil | $549.99-$1,899.99 |
| Ford 2.0 / 2.3 EcoBoost | Carbon, PCV, ignition coils | $349.99-$899.99 |
| Honda L15B (1.5T Civic, CR-V, Accord) | Fuel dilution misfire, plug fouling | $249.99-$549.99 |
| Honda K24 / K20 | Valve adjustment, VTC actuator | $249.99-$549.99 |
| Toyota 2GR-FE (V6 in pre-2012 Camry/RAV4) | VVT-i screen clog, carbon | $349.99-$899.99 |
| Toyota A25A (Dynamic Force 2.5) | Coils, plugs, occasional injector | $249.99-$799.99 |
| Chevy 5.3 / 6.2 V8 (AFM) | AFM lifter collapse, plug fouling | $3,499.99 (lifter) |
| Chevy 3.6 LFX / LGX V6 | Timing chain stretch, carbon | $549.99-$2,499.99 |
| Subaru EJ25 / FB25 | Plugs, coils, vacuum leaks | $249.99-$799.99 |
| Nissan VQ35 / VQ37 | Coils, plugs, VVEL actuator | $349.99-$1,099.99 |
| Hyundai / Kia Theta II 2.4 | Misfire from oil consumption / engine wear | Quote-only (recall coverage) |
Direct-injection engines have a fundamental design tradeoff: by spraying fuel directly into the cylinder, they achieve better fuel economy and power but lose the cleaning effect of fuel washing the intake valves. PCV oil mist baked onto the valves over years builds heavy carbon deposits.
Walnut blast service uses pressurized walnut shell media to physically blast carbon off the intake valves. The intake manifold is removed, each cylinder valve is rotated to closed position, walnut media is blasted into the intake port and vacuumed out simultaneously. The valves come out looking factory-clean. Service runs $549.99 and we recommend it preventively at 60,000-100,000 miles on direct-injection engines, or sooner if symptoms develop.
Vehicles where we routinely perform walnut blast: BMW N20, N52, N54, N55, S55, B58, S63; Mercedes M270, M274, M276, M157; Audi/VW EA888, EA113; Ford EcoBoost 3.5L, 2.0L; GM 2.0T LTG, LCV; Hyundai Theta turbo. Most other manufacturers added port injection to their direct-injection engines specifically to prevent this carbon buildup — Toyota 2GR-FKS for example uses dual injection.
Hunting idle is most often a vacuum leak, dirty throttle body, or failing idle air control system. The engine is trying to compensate for unmetered air or restricted airflow. Diagnostic identifies which.
Severely dirty — yes. A normally dirty air filter restricts power but rarely causes rough idle. We check air filter on every diagnostic and recommend replacement if dirty.
Most likely carbon-fouled intake valves on a direct-injection N20, N52, N54, N55, or B58 engine. The fix is walnut blast service at $549.99. We recommend this preventively at 60,000-100,000 miles. See our BMW repair page for full detail.
For mild fuel injector cleaning, yes — quality products like Techron, Red Line SI-1, or Lubro Moly Jectron run through the fuel system on a regular basis can help. They will not solve heavy carbon buildup on intake valves of direct-injection engines (DI engines need walnut blast for that). And they will not fix vacuum leaks, ignition issues, or sensor failures.
Throttle body cleaning at $189.99 if the throttle is the cause. Vacuum hose replacement starting at $149.99 if a hose is the cause. Diagnostic identifies which fix applies.
Mild rough idle — no. Misfires combined with rough idle — yes. Continuous misfire dumps unburned fuel into the catalytic converter and overheats it, eventually destroying the cat ($1,500-$2,500 each). Address rough idle promptly when accompanied by check engine light or P030X codes.
Engine running too rich — either over-fueling from a stuck-open fuel injector, failed fuel pressure regulator, or misfire dumping raw fuel into the exhaust. Diagnostic identifies which.
Yes. The MAF sensor tells the PCM how much air is entering the engine. A contaminated or failed MAF gives wrong air data, leading to wrong fuel quantity and rough idle. Cleaning $129.99; replacement $249-$499.
3-5 hours typically — intake manifold off, each cylinder valve rotated to closed, walnut blasted and vacuumed, intake reinstalled. Service interval recommendation: 60,000-100,000 miles on direct-injection engines.
Rough idle is uneven engine operation at idle. Misfire is a specific event where a cylinder fails to fire its combustion event — this throws codes and triggers check engine light. All misfires cause rough idle, but not all rough idle is from misfire.
1-2 hours typically. Includes scan tool data, smoke test, visual inspection, and any specific component tests indicated by initial findings.
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