The varied idle can be due to the bad gasket. It would likely leaking between cylinders and the engine then stops firing on two cylinders until it heats up and the head expands and the leak slows enough that the other cylinder comes back. It essentially loses the power from those two cylinders, slows down and then speeds up as the rest fire.
I would get it changed now, as the leak could easily cause it to hydro-lock and bend a rod/snap the crankshaft. Plus the unburnt fuel is probably washing the cylinder and you may end up replacing the engine, not just the head gasket.
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Monday, August 14th, 2017 AT 9:53 PM