Clumps of brown substance under radiator cap. I was thinking it is oil mixing with water which is what I filled up the cooling system with as im having a continuing issue with lower intake gasket not sealing. My vacuum readings are fluctuating from 11 to 14 inches. Engine shaking and stalling at idle. I just replaced rings and bearings. Am running a tfs stage one cam with pro comp heads. Compression test. shows150 psi in all cylinders. The only code is a 136 which is left side o2 sensor showing a lean condition.