At idle have exhaust fumes coming thru aircondition system on 2004 Lincoln LS

Was told it was the PVC hosing on top of engine...replaced...after 2 weeks same problem. Was also told the head gasket was NOT leaking. Smells like oil burning!

Asked by for the 2004 Lincoln LS
Check for oil leaking onto the exhaust system. Check the valve cover gaskets, as these are right above the exhaust manifolds