I recently, replaced the valve cover gaskets and intake gaskets on my 2004 v6 4.0 gas Ford Explorer and this didn't happen prior to replacing the gaskets. I found a vacuum line loose and not hooked up on the passenger side of the fender and it goes inside the firewall. I cannot locate where is hooks up now. Does anyone have a 2004 explorer they can share some pics to locate the vacuum hole hookup location.