How do you check for vacuum leak?

Hello, a technician using a diagnostic tool first would monitor fuel trims. If the engine is using tremendous fuel on both banks, then you likely have a vacuum leak. If you use propane (some folks use parts cleaner spray) to make "rich" with fuel the areas a vacuum leak may be present, the fuel trims will change, and the way the engine runs will change also. You would focus your attention on the areas you are directing this "fuel" towards. Naturally, this kind of diagnosis is something that a skilled technician with diagnostic equipment would carry out typically.

Using 'smoke machine' for testing is safest and most effective method .. Local repair shop should be equipped. Testing with flammables on a running engine is not recommended for the DIYer! .. As stated - "skilled technician" is your best bet - in any event. http://repairpal.com/repair-shops