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Q: 4th Cylinder misfire when start the engine

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The SES(Service Engine Soon) indicator of my car will be lighted when I START the engine, and some days later it will gone. Not sure why, but as of now I have had the same issue multiple times, light is on when start engine and then off after some days. I bought a diagnosis tool, every time I got SES, I used the tool to read the error code and it told me "4th Cylinder misfire", I have NEVER had the same issue when I actually drive the car, it just happens every time when I start the engine. I already replaced with new spark ignition as well as Ignition Coil, but still have the problem. Any comments here will be appreciated! Thanks!

My car has 90000 miles.
My car has an automatic transmission.

A: Eliminating the ignition coil and spark plu...

Eliminating the ignition coil and spark plug is a good start. Seeing as the misfire only occurs randomly and when cold leads me to believe you have a small vacuum vacuum leak or carbon build up on your engine valves.

Ensure your oil dipstick is sealing tight.

I would recommend having a fuel injection service performed on the vehicle first. Typically a 3-part service is recommended where additive is added to the fuel tank, a cleaning solution is ran through the vacuum side of the intake manifold (cleaning the valves also), and solution is run through the fuel injectors. This should take care of the possibility of carbon buildup hanging your valves slightly open.

Next I would have the vehicle checked for vacuum leaks. The vacuum leak can be diagnosed with a smoke diagnostic machine or using a scan tool with data values and monitoring the oxygen sensor values while spraying around the intake and vacuum lines with carburetor cleaner. The 1.6L engine also had a problem in the PCV system which caused an internal vacuum leak. The PCV valve is integral to the valve cover, which requires replacement of the whole valve cover. To test for this condition a sensitive vacuum gauge is hooked to the oil dipstick tube and with the engine running the value should be under 10 mBar. If over, you need a new valve cover. I have done several of these with less than 60,000 miles.

Finally if the problem is still there, I would perform a cylinder leak-down test on that cylinder to check the engine valves for leaking. This requires a special tool, compressed air, and service information.

I tried to list the suggestions in easiest and most likely fixes to harder and least likely fixes. As you see most of the diagnostic procedures require special tools. If you would like to have the misfire diagnosed, you can contact a professional technician, such as one available from YourMechanic.

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