QuestionWhile driving, usually accelerating, the car suddenly stalls. Happens on average once per day. Sometimes after 5 minutes of driving, sometimes 60 minutes. Not repeatable. Always starts right up immediately after stalling. Took to mechanic. Passed all engine tests, road tests, etc. Recently replaced starter and alternator. Only suggestion from mechanic is the crank sensor but they have no evidence this is the problem. Thoughts? Thanks!
AnswerHi Lou,
I'll assume you have the 2.5L V-6. The problem sounds like it has to do with mixture rather than with spark because it always comes back to life immediatiely. That would not be the case if it were the spark coil, rotor, or crank/cam sensors.
One of the common causes is an exhaust gas recirculation valve that is stuck ajar rather than being closed at startup, idle, and full throttle when it exhibits the jerkiness.
So you need to check that and if so try and get it freed up and moving again so that it will be closed when the engine is shut down, otherwise it will be difficult to start and to idle or accelerating which also need for the valve to be closed.
The first thing I would do is check the mechanical function of the egr valve which is located along a pipe that runs from the left exhaust manifold (on the side of the engine facing the front of the car) to the intake manifold area (where the incoming air in the large rubber tube enters the throttle). That valve is metal and has a round fitting with a vacuum hose attached, mounted on the top of the valve, and the round part is attached to the main body of the valve by a sort of saddle. Inside the open saddle you will see a metal rod (with a slot) that connects the round top fitting to to the valve body. That rod is a stem on the valve and it is supposed to go in and out in response to the engine vacuum which varies with RPM and throttle opening (gas pedal position). Take a spray can of WD-40 or other penetrating lubricant and spray the stem where it enters the valve body and then use a regular screwdriver blade tip inserted in the slot to lever the valve in and out to try and free up its motion. Also check all the rubber vacuum hoses associated with the valve and a nearby vacuum solenoid valve. If the valve seems to open (against the action of a spring) and close firmly by the spring action when using the screwdriver blade to facilitate the motion, then you should be able to start the engine. You can, once it is idling, check that the valve stem moves when you rev the engine from idle to 2500 rpm and back to idle.
Then see if that clears up the problem. I assume the mechanic checked for fault codes and found none. If you get a persistant check engine light then that would mean that there is some problem that has been identified and that would be a good time to readout the controller for fault codes. I can tell you how to do that yourself, or you can get a reader to borrow at Autozone. It may be one of the sensors is off-value but not so far as to set a fault code in the controller.
Until a code is set about all you can do is check the function of those items that are pretty easy to do: the throttle position sensor (measure the resistance between the center and either side pin while varying the throttle valve to make sure there are no discontinuities), the vacuum lines that are attached to sensors such as the MAP, egr solenoid, and to other pollution control devices (vapor recovery, for example). You might try shaking the harnesses when at idle to see if movement might cause a die out, in which case you could trace to see which items in the harness are engine control related and check the connections of those wires.
I hope one of these suggestions bears fruit for you.
Roland
