I have a 01 corolla with 160,000 miles. Everytime i turn on the ignition, I hear a high pitch noise. Replaced the spark plugs and ignition coils. Could it be a vacuum leak? Where would I check for vacuum leaks?
Can you feel the engine missing?
Take a can of WD40 and with the engine at idle, spray around where you think the leak might be. When you do hit the leak, the WD40 will make the engine speed up slightly, then you have found your leak.
I like to use a small propane torch can with a rubber hose attached, WD40 is cheaper, easier to find and less flammable.