code p0300, timing chain job replacement?

2007 FORD F-150
200,000 MILES • 5.4L • V8 • 4WD • AUTOMATIC
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AGILL
Recently completed a timing job on the truck listed above. Everything replaced was ford parts. Started truck up after completion and it sounded great and started with no issues. Ran good until the motor got hot. Then started running rough and sounds like it is missing. Check engine light did not come on. Hooked my scanner up anyway and got code p0300. Cleared code. Let truck sit. Tried to drive it the next day, same thing went down the road good with no issues until it got hot and it did the same thing, running rough, had to stop and let it sit. After it cooled off cranked back up fine and drove it back home. No check engine light, checked with scanner and same code p0300. Started it the next day in the yard and it ran fine until the motor got hot and then it did the same thing. Same code p0300 and no check engine light. Where/what should I start with now.
Aug 16, 2025 at 1:19 PM
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STRAILER
  • ASE Certified Mechanic
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  • ASE Certified Mechanic
I random misfire can be a vacuum leak or the MAF sensor needs to be replaced. The vacuum line at the rear of the intake manifold is a tough one to reconnect when reassembling. Also, when you had it part did you service the throttle bore? Here is a video I would follow to see if the engine is leaking vacuum:

https://www.youtube.com/watch?v=LRKWV4Are5c

This guide may help as well:

https://www.2carpros.com/articles/automotive-engine-misfire-code-p0300-causes-and-solutions

Please go over these guides and get back to us.
Aug 16, 2025 at 8:18 PM
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