Why is my car misfiring and stalling after changing spark plugs?
Replacing spark plugs and ignition wires can leave a car running roughly, dropping to a very low idle and dying unless the choke is on. This happens when the underlying cause of the misfire wasn't fixed by the new parts, preventing the engine from running smoothly on its own.
What the numbers show
Counted from the threads quoted below. How we count
- People have been saying this in most months since September 2026.
- This comes up 12.2× more often in r/MechanicAdvice than across the site as a whole.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
Why is my car misfiring and stalling after changing spark plugs?
- 1Using the choke to keep the engine runningDid this help you?
- 2Removing and reseating HT leadsDid this help you?
- 3Reinstalling old plugs and leadsDid this help you?
- 4Replacing ignition coils, spark plugs, and fuel injectorsDid this help you?
- 5Checking engine compressionDid this help you?
- 6getting the car scanned at an auto parts storeDid this help you?
- 7asking a friend who is a campus mechanicDid this help you?
- 8hiring a mobile mechanic for a diagnosisDid this help you?
- 9swapping spark plugs between cylinders to testDid this help you?
- 10buying and replacing fuel injectorsDid this help you?
- 11buying new spark plugsDid this help you?
- 12Replacing the remaining spark plugs and coil packsDid this help you?
- 13Checking for debris in the spark plug wellsDid this help you?
- 14Verifying connections and parts installationDid this help you?
- 15Replacing the spark plug again as a temporary fix to stop the shakingDid this help you?
- 16Swapping ignition coils between cylinders to see if the misfire follows the coilDid this help you?
- 17Checking if spark plugs are tightened properlyDid this help you?
- 18Verifying the spark plug gap is correctDid this help you?
- 19Inspecting new plugs for cracked porcelain before installationDid this help you?
- 20Checking that ignition coils are plugged in correctlyDid this help you?
- 21Ensuring the correct brand and type of spark plugs were usedDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“I recently changed the spark plug/HT leads... and basically the car is running like a dog.”source ↗
“It runs ok with the choke on, but if I push the choke in it starts to misfiring badly and with the choke off basically drops to ~400rpm idle and then dies”source ↗
“My partner had an engine oil leak so I've tried to be the "man", replaced engine valve cover and spark plugs and now I'm so disappointed because it's misfiring I guess?”source ↗
“so today i bought new spark plugs because i was like what the heck i gotta figure something out but im still getting those two issues and the check engine light, so at this point i don't know what to do because im a broke college student who can't really afford to buy a new engine or a new car so if you got any suggestions please send them my way.”source ↗
“I only did my front 3 spark plugs and coil packs because the 6 cylinder was misfiring. Why is it acting like this now?”source ↗
“Replacing these item did not fix the issue.”source ↗
“After replacing the fuel injector, the P0301 code has disappeared, but the engine is still running roughly and feels the same as it did before.”source ↗
“Any suggestions on what I should test next would be greatly appreciated.”source ↗
“Started misfiring, so I got some NGK's and it ran beautifully again. 10 days later, right back to where we started.”source ↗
“Replaced the spark plug again temporarily and it's fine again, but I know I still need to get down to the bottom of this.”source ↗
“Car was shaking until I replaced that spark plug and it immediately went away.”source ↗
Where this came up
People with this problem also raised
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