[s-cars] head gasket blown

[Twobro12 at aol.com]

Hey, i recently posted a list about a possible head gasket failure.  I brought my car to my mechanic and he said that if I had blown my head gasket, I'd be leaking coolant and should see smoke coming from the exhaust.  These are not my symptoms though: I am getting strange vibrations/possible knocking of engine even at idle, and it only occurs sometimes after the engine has fully heated (to average temp.)  My mechanic did some diagnostics and Vag-com brought up error codes that says one of my speed sensor parts or something to that degree had failed, and he got no readings of engine gasket failure.  anybody else have a say on this?  is the computer reading reliable enough to just go with that?

mike 94 S4 with almost 100k miles