Parts
$20–400
P0300 — Random / Multiple Cylinder Misfire
STOPIs it safe to drive? A misfire dumps raw fuel into the exhaust and can overheat and destroy the catalytic converter fast. Heavy shaking under load is a tow-it situation.
What P0300 means
The computer detected misfires it couldn't pin to one cylinder — combustion is failing or incomplete across several. Often felt as a rough idle, shake, or stumble.
Most likely causes (in order)
- Worn spark plugs or ignition coils (start here)
- Vacuum leak leaning out several cylinders
- Weak fuel pump / clogged filter / dirty injectors
- Low compression (timing, valves, head gasket)
- Bad plug wires (on older engines)
Symptoms you might notice
- Rough idle / shaking
- Stumble or hesitation on acceleration
- Flashing check-engine light = active damage
What to check first
A FLASHING light means it's misfiring right now and cooking the cat — stop. Pull the cylinder-specific codes (P030x) and a misfire-counter; swap a coil to a known-good cylinder and see if the misfire follows it.
Repair cost & difficulty
Labor
1–4 hr
Difficulty
DIY-friendly