Making a diagnosis based solely on previous experience can save a lot of diagnostic time, but it can also lead to some very wrong conclusions. If you’ve done any work on European cars, you have probably replaced your share of idle stabilizer valves to cure a wide range of driveability complaints. Replacing the idle stabilizer valve seemed like the obvious fix for an Audi with a higher than normal, out of control idle speed that is the subject of this month’s Driveability Clinic. However, playing the percentages wouldn’t have paid off this time around.