Symptoms / Engine misfire (skipping, stumbling, or a dead cylinder)
Engine misfire (skipping, stumbling, or a dead cylinder)
Address promptlyA misfire means one or more cylinders aren’t burning their fuel — the codes usually name the cylinder, which makes this unusually diagnosable.
What this usually means
Each cylinder needs three things to fire: spark, fuel, and compression. A misfire is any cycle where one of the three falls short and the cylinder contributes nothing — felt as a stumble, a rhythmic shake, lost power, and often a check-engine light. What makes misfires more tractable than most engine problems is that the computer counts them per cylinder: a P0301 means cylinder 1 specifically, P0300 means misfires scattered across cylinders. A single-cylinder code points at that cylinder’s own parts (plug, coil, injector, compression); a random-misfire code points at something shared, like fuel pressure, a vacuum leak, or exhaust restriction. That one distinction, read from the codes before any parts are bought, is the backbone of an efficient diagnosis.
Most likely causes
- highWorn or fouled spark plugsThe most common cause and the cheapest fix. Electrodes erode with mileage until the spark can’t reliably jump, especially under load.
- highFailing ignition coilCoils fail one at a time on modern coil-on-plug engines, producing a persistent single-cylinder misfire. Swapping the suspect coil to another cylinder and seeing if the code follows is the standard test.
- mediumClogged or failed fuel injectorA restricted injector leans out its cylinder; a dead one stops it entirely. Single-cylinder misfires that survive new plugs and coils often end here.
- mediumVacuum leak or lean conditionA shared lean mixture causes random misfires across cylinders, usually worst at idle, and often comes with lean codes alongside the misfire code.
- lowLow compression (valve, rings, or head gasket)If the cylinder can’t hold pressure, no ignition part will fix it. A compression or leak-down test is the definitive check when the usual suspects are exhausted.
Is it safe to drive?
Typical fix & cost
Read the codes first: a numbered cylinder code narrows the work to one cylinder, where plug, coil, and injector get checked in that order — coil-swap tests make this fast. Random misfires get the shared systems checked: fuel pressure, vacuum leaks, intake. Most misfires resolve with plugs, a coil, or an injector; compression-related misfires are the rare, expensive tail.
Typical range: $100–$1,000
A set of plugs is the low end, a coil or injector the middle; compression-related repairs (valves, head gasket) exceed this range and get quoted separately once confirmed.
The price depends on which cause it turns out to be — so confirm the cause before paying. Diagnose this for my exact vehicle →
Frequently asked
What does the cylinder number in a misfire code actually tell me?
P0301 through P0308 name the specific misfiring cylinder, which localizes the problem to that cylinder’s plug, coil, injector, or compression. P0300 (random/multiple) means the cause is shared — think fuel pressure or a vacuum leak rather than one bad part.
Can I fix a misfire by just replacing all the spark plugs?
Often, yes — plugs are the most common cause and due by mileage anyway. But if the misfire persists, resist replacing parts in bulk; a coil-swap test or injector check pinpoints the fault for less than a set of coils costs.
Will a misfire go away on its own?
Rarely, and intermittent ones usually return worse. Meanwhile every misfiring cycle pushes unburned fuel into the catalytic converter. Even a miss that comes and goes deserves a diagnosis.
Seeing this on your car? Get a diagnosis specific to your exact year, make and model — RedlineAi ranks the likely causes against real recall and complaint data, with an honest confidence score.
Diagnose my vehicle →Related OBD-II codes
If your car has stored a trouble code, these often accompany this symptom:
Related symptoms
This is general guidance, not a substitute for a hands-on inspection. Cost ranges are broad estimates to set expectations, not quotes. For safety-related issues, have the car inspected by a licensed mechanic before driving.