A warm rough idle and multi-cylinder misfire counters appeared together, while the engine smoothed out above idle.
Why this matters
The value of this case is the order of evidence and the verification step. The same symptom on another vehicle may have a different cause.
Evidence to capture first
- Freeze-frame load and temperature
- Cylinder counters
- Fuel trim at idle and raised rpm
- Low-pressure smoke at the manifold joint
A disciplined path
- Preserve the code data
- Compare trim by rpm
- Confirm the leak visually with smoke
- Reseal the joint and repeat the warm-idle test
Decision point
The repair was supported by a visible leak, corrected fuel trim, and stable misfire counters—not by the P0300 label alone.
Source desk
Use current model-specific service information for specifications, connector locations, disabling procedures, and tightening values. The following public resources support the broader safety or system context used in this guide.
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