The short answer: rough idle in a G35 is most often caused by a misfire, a vacuum leak, or an idle-control issue, with worn motor mounts or weak fuel delivery as possible contributors.
In more detail, idle shaking can stem from ignition problems, air or fuel delivery issues, and mechanical or mounting wear. This article explains the common causes, how to diagnose them, and practical steps to get your Infiniti G35 running smoothly again.
Common causes of shaking at idle on a G35
These are the frequent culprits to inspect first.
- Engine misfire caused by worn or fouled spark plugs, failing ignition coils, or damaged coil-on-plug boots
- Vacuum leaks from cracked hoses, intake manifold gaskets, PCV valve, or the brake booster line
- Dirty or failing Idle Air Control Valve (IAC) or dirty throttle body that prevents stable idle
- Faulty or dirty Mass Air Flow (MAF) sensor or air intake issues
- Weak fuel delivery: low fuel pressure or clogged/injectors
- Sticking or failing EGR valve or related vacuum lines
- Worn engine mounts or broken motor mounts causing excessive vibration at idle
Each of these can cause rough idle or shake. A systematic check is needed to identify the actual cause on your G35.
Diagnostic steps
To pinpoint the issue, follow a structured diagnostic approach and use basic tools and OBD-II data when available.
- Scan for trouble codes and review misfire indicators (P0300-P0308 or cylinder-specific codes). Note any pending codes and abnormal sensor readings.
- Inspect the ignition system: remove and inspect spark plugs for wear or fouling, and test ignition coils or coil packs. Swap suspected coils to see if the misfire follows a particular coil.
- Check for vacuum leaks: listen for hissing, inspect hoses for cracks, and gently spray a small amount of brake cleaner around suspect joints while the engine idles to see if RPM changes (avoid flames and avoid contact with hot surfaces).
- Inspect the Idle Air Control Valve and throttle body: clean carbon buildup, ensure idle speed is within spec, and check for a sticking throttle plate or irregular idle.
- Test the MAF sensor and air filter: clean the MAF with proper cleaner or replace a dirty air filter; check for air intake leaks after the filter housing.
- Check fuel delivery: verify fuel pressure with a gauge, inspect the fuel filter, and consider injector cleanliness if fuel delivery seems weak or inconsistent.
- Evaluate engine mounts: with the engine running and the transmission in Park, observe engine movement after a quick rev. Replace cracked or worn mounts as needed.
- Consider other sensors if the problem persists: TPS, crankshaft/camshaft position sensors, or the EGR valve’s function and vacuum lines.
These steps help narrow the cause; if you cannot identify or safely perform tests, seek a qualified mechanic for a thorough diagnostic.
When to seek professional help
Rough idle can sometimes signal more serious issues that require specialized tools or expertise, especially if fuel pressure testing, ignition coil testing, or complex sensor troubleshooting is needed, or if a check engine light remains on.
Summary
Idle shake in a G35 is commonly tied to misfires, vacuum leaks, idle-control or airflow issues, fuel delivery problems, or worn engine mounts. A practical diagnostic path—scanning for codes, inspecting ignition and vacuum systems, cleaning or testing the throttle/MAF/IAC, and assessing fuel delivery—will usually identify the cause. Keeping up with regular maintenance, such as spark plug replacement, coil checks, and clean air/fuel components, helps prevent rough idle and keeps the G35 running smoothly.