It's coolant leaking into the cylinders. Still no coolant in oil either. There is an easy and free way to diagnose. Step 1, immediately after turning off your completely warmed up engine, (200 F), completely unscrew coolant cap, (*VERY SLOWLY AND EXTREMELY CAREFULLY BECAUSE THE COOLANT IS EXTREMELY HOT AND WILL BE UNDER A LOT OF PRESSURE AND WILL SERIOUSLY BURN YOU IF YOU DON'T USE CAUTION*), but leave on to keep foreign debris out. Step 2, let sit for 4 hours or longer, even overnight, with cap unscrewed ( basically want to reproduce the situation when it idles rough, but the coolant pressure is the variable). STEP 3, after sitting for prolonged period, start car. If it no longer idles rough after start up, you are leaking coolant into cylinders.
Friday, October 30th, 2015 AT 9:34 PM