I have been having rough idle problems and have found a lot of useful threads about diagnosing the problem in my 1992 BMW 525i E34 M50. After reading them I went under the hood and ended up finding some loose, hardened and brittle vacuum hoses in the area of the intake.

I am interested in replacing my vacuum hoses with those colored silicone hoses. I know a lot of Porsche guys do that. I looked for an archive on this and could not find any. Can anyone direct me to an archive on them? Specifically, do they commpare to OEM in terms of performance, and longevity? Does anyone know the size of the vacuum hose reuired for my engine? I heard that they are 3.5MM or 8 MM hoses.