FixCar Running Rough or Misfiring — What It Usually Is
Rough running — shaking at idle, stumbling under load, lost power — is almost always ignition or fuel delivery on one or more cylinders. The fix pattern is dominated by two parts that wear together.
What it actually turns out to be
| The fix involved | Share of visits* | Typical cost† | Median |
|---|---|---|---|
| Spark Plugs | 42.4% | $170 – $474 | $296 |
| Ignition Coil | 30.5% | $184 – $402 | $269 |
| Fuel Filter | 8.9% | $134 – $436 | $256 |
| Sensor | 6.7% | $180 – $433 | $287 |
| Fuel Injectors | 6.7% | $164 – $697 | $343 |
| Distributor | 4.5% | $242 – $533 | $388 |
| Valve Cover Gasket | 4.4% | $182 – $481 | $299 |
| Oxygen Sensor | 3.8% | $212 – $435 | $304 |
| PCV Valve | 3.5% | $85 – $268 | $152 |
| Other, rarer causes | smaller shares | varies | — |
*Share of visits whose repair involved this part. Combined repairs count toward each
part involved, so shares overlap and don't add up to 100%. Among visits that ended in a parts repair.
†Middle half of real invoices (25th–75th percentile) when this was the only fix — parts + labor, all vehicle types.
Real repair reports
These are recent, paid visits for this complaint — the words as the owner said them, and what it turned out to be.
Car owners said
“Diagnose why vehicle has no power”
“Misfire on cyl 3”
“Has a misfire code”
“Tow in no power”
“Diag - running rough”
“Runs rough at times”
Shaking with a flashing check-engine light
That's an active misfire. Ignition coils and spark plugs lead these outcomes by a wide margin — and shops often replace plugs alongside a failed coil, since worn plugs are what overworked the coil.
Rough only at idle
Smooths out when you rev? Vacuum leaks and idle-control carbon are the usual suspects — a different, usually cheaper family than misfires.
Rough under acceleration
Stumble under load with normal idle points at fuel delivery — filters, pumps, injectors — or breakdown in coils that only shows under demand.
Costs by vehicle
- Ignition Coil: Ford F-150 · Ford Expedition
- Spark Plugs: Ford F-150 · Chevrolet Silverado 1500
- Oxygen Sensor: Ford F-150
- Car Battery: Ford F-150 · Chevrolet Silverado 1500 · Toyota Camry
Take this to the shop
The FixDozer Diagnosis Brief puts this page on one printable sheet: what this complaint usually turns out to be, how often, and what each fix should cost — so when the diagnosis comes back, you already know whether the number fits.
Download the Diagnosis Brief (PDF)View it online · Narrow it down for your vehicle