QUOTE (batrachian @ Mar 5 2010, 12:44 PM)
I suspect there is a vaccum leak somewhere and I need to find it out since the car has rough idle lately. After searching the forum, I have yet seen a recommended way of doing it. Could somebody please shed some light on this?[/b]
Do a search for codes P0171 and P0174. If you have a vacuum leak bad enough to cause idling problems you should have a CEL
. If so follow the write ups for those codes. Usually 3 or 4 ways to find a vacuum leak. One visually check all rubber hoses for cracks, especially those going to and around the PCV
. Two disconnect and cap the main vacuum source from the engine to the vacuum box on the firewall. If the engine then runs good your vacuum leak is in other areas than the engine, such as EVAPS, brake booster, or all your heating and airconditioning controls (DO NOT DRIVE YOUR CAR WITH THIS LINE CAPPED OFF< YOU WILL NOT HAVE BRAKES). Next you can use spray starter fluid, spray brake cleaner, or propane and spray around hoses, upper and lower intake, etc. If engine runs better when you get to a certain area you have found your leak. For those who get those codes but really do not notice any performance issues it gets a little harder. If you have a engine code reader that has the Live Data function you can monitor the Short Term Fuel Trim Levels as you spray around the engine. If you get near a leak the levels should move closer to zero or go lower. For your rough idle also check the operation of your EGR
system. If you are really sure you have a vacuum leak and can't find it, you can go to a garage that has a smoke machine that will find it rather quickly. Hope this helps.