Intermittent driveability problems of any kind are always a challenge to diagnose. When a customer brings you a vehicle and complains of a stalling problem, you may not have much to go on other than their description of what's happening and when it happens. The more information you can get out of them the better, because you'll likely need as many details as possible to narrow down the list of potential causes.

Many times, there will be no check engine light and no fault codes to give you a clue as to what might be causing the engine to stall. So the trick to diagnosing an intermittent stalling problem is to catch the vehicle when it's acting up - and that rarely happens when you have the vehicle in your shop. You may have to keep the car and drive it for a few days to see if it stalls. Or, if you have a flight recorder, you can hook it up to the car and send your customer home with instructions on how to catch a snapshot of the problem when it happens. But even then, you may not capture any usable data.

COMMON CAUSES
Common causes of intermittent stalling may include a bad idle speed control (ISC) system, low fuel pressure, loss of ignition, vacuum or EGR leaks, or other problems we'll get to later in this article. The engine's idle speed is controlled by how much air is allowed to bypass the throttle via the idle bypass circuit in the throttle body. The PCM monitors idle speed and operates a solenoid or small ...