Car has been stuttering on initial startup when engine is cold. It is becoming progressively worse and just today it took a while before i could start it. After I started it and let it run for a while to warm up, turning it off and on is normal. I put sea foam into the gas tank to clean up any buildup that could be causing it. I do have a check engine light for knock sensors which i have ordered but did not install yet and may be causing or adding to the problem. what are some common things based on the symptoms that could be causing this?
My car has 191000 miles.
My car has an automatic transmission.
Hello - a "hard start when cold, or left overnight" is usually a fuel mixture problem during cold start. The coolant and air temperature sensors cause problems when they do not accurately measure coolant and air temperatures, report bad temperature information to engine management, and cause either a "too rich" or a "too lean" mixture condition. A failing fuel pressure regulator or fuel pressure check valve can cause low fuel pressure issues, but that is usually resolved in less than a minute or two after engine startup. Re-starting during the day for all of these conditions will tend to be more normal. I recommend a hard starting inspection performed by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, narrow this diagnosis, and give you an accurate assessment of damage and cost estimate for repairs.
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