Diagnosis Brief
what this complaint usually turns out to be
what this complaint usually turns out to be
Car Running Rough or Misfiring — What It Usually Is
How real visits for rough running ended at independent shops across the US — the part actually replaced, how often, and what it cost when it was the only fix.
Spark plugs or ignition coil
Nearly half of all these visits end in one of these two
Spark plugs $170 – $474
Ignition coil $184 – $402
typical cost when it was the only fix
(parts + labor)
(parts + labor)
| The fix involved | Share of these visits* | Typical cost† | Median |
|---|---|---|---|
| Spark plugs | $170 – $474 | $296 | |
| Ignition coil | $184 – $402 | $269 | |
| Fuel filter | $134 – $436 | $256 | |
| Sensor | $180 – $433 | $287 | |
| Fuel injectors | $164 – $697 | $343 | |
| Distributor | $242 – $533 | $388 | |
| Valve cover gasket | $182 – $481 | $299 | |
| Oxygen sensor | $212 – $435 | $304 | |
| PCV valve | $85 – $268 | $152 | |
| Other, rarer causes | smaller shares — vacuum leaks, EGR valves, mass-airflow sensors, throttle bodies | varies | — |
*Share of visits whose repair involved this part; combined repairs count toward each part, so shares overlap and don't add to 100%. †Middle half of real invoices when this was the only fix — parts + labor, all vehicle types.
Which one is yours? Listen first
- Shaking with a flashing check-engine light — That's an active misfire.
- 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.
What to expect from the shop
Rough running almost always sets a misfire code that names the cylinder — a good shop swaps the coil or plug to confirm the culprit before replacing it. Plugs and coils are the common answers; injectors and fuel pumps the pricier ones. If the quote is a full set of coils on a single-cylinder misfire, ask why.
About this data · How to use this brief
Vehicles all makes and models, US fleet
Data confidence High — large sample, stable shares
Records through July 2026, refreshed continuously
Source paid invoices from independent US repair shops
Data confidence High — large sample, stable shares
Records through July 2026, refreshed continuously
Source paid invoices from independent US repair shops
Take it to the shop. It tells you what the likely answers are and what each one should cost — so when the diagnosis comes back, you already know whether the number fits. Vehicle-specific price reports for the common fixes are on fixdozer.com.