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Q: Losing coolant, high idle rpm, 2x P0300 1x P1111

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Hello, I've been having some trials with my '05 Sentra SE-R Spec V lately. My idle rpm has been fluctuating between roughly 700 and 1600 revolutions per minute, and the car is quite loud. More importantly, I'm losing a lot of coolant from my reservoir with no visible leaks. I am suspecting a head gasket or intake manifold gasket. The hard part is figuring out exactly which one and if my rpm problems are related or not. My oil and coolant are not mixing and the misfire occurs on startup, particularly with a hot engine.

I do not have any equipment to pressure test the cooling system and am lost on where to turn. I'd like to figure out exactly what is wrong with it and what options I have available. Do you have any advice or tips?

My car has 194000 miles.
My car has a manual transmission.

Hello. From what you describe it would appear that there may be more than one issue with the vehicle. The rpm fluctuations can be caused many different things. A few things I would check are the idle air control valve, and the any vacuum lines for the possibility of a vacuum leak. Coolant loss with no visible leaks can be difficult to diagnose. It may be possible for you to rent a cooling system pressure test kit from an auto parts store, sometimes even free of charge. A cooling system pressure test would be best way to determine if there is any internal, or external oil leaks.

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