Engine & warning lights
Engine Misfire P0300: Why Your Car Shakes Under Acceleration
Understanding P0300 and P0301–P0306, how to isolate the failing cylinder, and what the repair costs.
The short version
$10–32 per plug, $40–120 per coil, $55–130 for injector cleaning; low compression means internal work starting around $800.
- 4 symptoms you can check yourself
- 4 diagnosis steps in order
- 2 FAQs answered directly
- Last editorial review: 2026-08-01 · 6 min read
Overview
P0300 means a random misfire across cylinders, while P0301 and up name a specific cylinder. Misfire dumps unburnt fuel into the exhaust and overheats the catalytic converter fast.
Key takeaways
- Rough idle or shaking at steady cruising speed
- Worn spark plugs or incorrect plug gap
- Scan and check whether the misfire is random or cylinder specific
- Not quickly, but it will kill the catalytic converter, which costs many times more than plugs.
Symptoms
- Rough idle or shaking at steady cruising speed
- Clear power loss and delayed throttle response
- Check engine light flashing under load
- Popping from the exhaust and a fuel smell
Likely causes
- Worn spark plugs or incorrect plug gap
- Weak ignition coil on one cylinder
- Clogged or leaking fuel injector
- Intake vacuum leak or low cylinder compression
Diagnosis & repair steps
- Scan and check whether the misfire is random or cylinder specific
- Swap the coil with a neighbouring cylinder and rescan — if the code moves, the coil is the fault
- Read the plugs: white or oily black tips indicate a mixture problem
- If the code stays on the same cylinder, run a compression test
Expected cost
$10–32 per plug, $40–120 per coil, $55–130 for injector cleaning; low compression means internal work starting around $800.
Figures are a guidance range calculated with a published method — read the methodology.
Run your own estimateHow to prevent it
Replace plugs on the correct interval (copper ~20k mi, iridium 60–70k mi) and use an injector cleaner every 6,000 miles.
FAQ
Will a misfire destroy my engine?
Not quickly, but it will kill the catalytic converter, which costs many times more than plugs.
Why does it only misfire when cold?
Usually weak plugs or a small vacuum leak that seals once components expand with heat.
DriveMet review
$10–32 per plug, $40–120 per coil, $55–130 for injector cleaning; low compression means internal work starting around $800. Replace plugs on the correct interval (copper ~20k mi, iridium 60–70k mi) and use an injector cleaner every 6,000 miles.
What we verified
- Cross-checked 4 warning signs against 4 likely causes before publishing.
- Reviewed 4 repair steps and confirmed the order a shop would follow.
- Compared the cost range with our published methodology and refreshed it on 2026-08-01.
- Answered 2 questions people actually search for on this topic.
Reviewed by the DriveMet editorial team on 2026-08-01 under our editorial policy. This is an editorial review of the page, not visitor ratings.
Related tools
Apply what you just read to your own car with your own numbers.
Reference sources
- NHTSA vPIC — vehicle specifications and manufacturer recalls
- EPA fueleconomy.gov — reference fuel-economy figures
- SAE J1979 standard for generic (Pxxxx) fault-code definitions
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