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Q: high idle when hot and missfire all the time.

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so I replaced a blown head gasget and now I know I timed it correctly but I put it back together and now I am getting check engine code p0300,p0301,p0303 I see white smoke out of the muffler and it smells of burnt oil and idles at 2000rpms and has a missing fire sound. when cold not as often misfire sound and 800rpm idle. I checked the pcv valve and it is fine. its not getting hot. idk what to do? thanks.

My car has 207000 miles.
My car has an automatic transmission.

If you overheated the engine prior to replacing the head gasket you would need to have the head checked for cracks and get the surface refaced. If this has been done, then the problem may be that the cylinder block is cracked, or you have not put something together properly and have a vacuum leak. The left over coolant in the exhaust from the previous overheating may be the reason for the smoke which will eventually go away.

Check the cooling system and engine for overheating again, if so, then you will need to find where the coolant is getting into the cylinders. A certified mechanic would be able to diagnose the symptoms you’ve described to in order to fix your misfire and high idle issues.

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