F150 Ecoboost misfire at idle but fine under acceleration
The engine misses noticeably on cold starts and low RPMs—sometimes stalling when coming to a stop—but has no issues during acceleration or highway cruising. Because the misfire counts are often too low to trigger a check engine light, identifying the problem requires looking at average cylinder acceleration to find the specific failing cylinder. Without thorough diagnostic testing, shops may just throw parts at the problem, quoting around $4,000 for camshaft and timing chain replacements.
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.
- 1Checking cylinders for signs of coolant to rule out head gasket issues.Did this help you?
- 2Swapping the spark plug from cylinder 1 to another cylinder to see if the misfire follows the plug.Did this help you?
- 3Replacing the spark plugsDid this help you?
- 4Replacing the oil separator or PCV valveDid this help you?
- 5Checking for carbon buildup on the intake valvesDid this help you?
- 6Cleaning the coil pack ground wiresDid 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.
“When it warms up 10 seconds the idle gets significantly better but there’s still a noticeable miss”source ↗
“it only shows the major spikes during acceleration but I never feel a miss during acceleration the engine light is not on and never cuts on for misfire”source ↗
“It won’t read a misfire count it’s not enough to draw a code, when I do the average cylinder acceleration ever cylinder sits close to 0 except 1 average is at -4”source ↗
“Check engine light is for misfire on all cylinders (P0301,2,3,and 4) with no other codes. It is intermittent and only at idle or low RPM.”source ↗
“Sometimes is bad enough to stall when coming to a stop. No issues under acceleration or cruising at highway speeds.”source ↗
“Had a shop look at it and they said it “could” be a bad camshaft and I need a timing chain replacement while they are at it and quoted right under $4k. They barely looked at so I am not convinced that they aren’t trying to just throw parts at it.”source ↗
Where this came up
People with this problem also raised
- 25Engine misfires and RPM surging when driving uphill
- 5Why is my car revving so high on a cold start?
- 11Why does my car stall when I step on the gas?
- 68Why does my car make a loud rattle when starting the engine?
- 3Cylinder misfire and white smoke from exhaust
- 2Why does my car take so long to warm up and blow cold air?