When I first start my car the engine makes a loudish and consistent knocking sound coming from the upper half of the engine on the drivers side. None of the vales seem loose and I've checked for leaks and can't find any. After around 5 minutes of running the rpms lower and the knocking stops. When I accelerate hard ito starts knocking again, but only during the time I'm using the gas pedal. With the misfires it's fine on idle and startup but is only an issue on accelerating and coasting. Such as when I'm on the freeway and let off the gas a little, or starting from a stop at a red light. The service engine/check engine light has not come on at anytime the misfires occur. The light does work though as I've put the key in the 2nd position, without starting the car, and the light works during the testing phase. The misfires are always an issue on acceleration whether or not the car has been running for a while. I've replaced the spark plugs, cleaned the throttle body, and used fuelcleaner
My car has 152687 miles.
My car has an automatic transmission.
The noise in the engine may be from running with the ignition timing too far advanced from a malfunctioning mass air flow sensor. The mass air flow sensor could be giving false readings, which will cause the computer to compensate by injecting less fuel into the engine. This will cause the engine to knock and run with less power and may misfire due to the issue. Have the vehicle computer scanned and take a data reading of the mass air sensor to see if it is reading the metrics. If it is incorrect then you may not get codes but will need to have the mass airflow sensor replaced. If you need assistance in diagnosing this issue, a certified YourMechanic technician can come to your location to inspect your engine misfire.
Have a car question? Get free advice from our top-rated mechanics.
Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Save up to 30%