Sometimes the engine will cut out very briefly right as I press the gas pedal. This Subaru service bulletin explains what can cause this problem:
HESITATION ON ACCELERATION - 11-53-98 (2/99)
Applicability: 97-98 Legacy, Impreza, and Forester Manual Transmission Vehicles with 2.5l and 2.2l engines.
In the event you encounter a customer complaint of a slight engine hesitation between 1500-2500 rpm's when the engine is cold or hot, perform the following
Eliminate all external influences, such as an incorrect or dirty air filter, loose or tracked intake duct, dirty fuel filter, low fuel pressure, PVC system, or low engine vacuum that would indicate an external leak or an internal engine component.
If all external components are confirmed to be operating within vehicle specifications, the hesitation may be caused by the ignition control logic in the ECM. Under certain low rpm driving patterns, the ignition control system can pick up engine vibrations through the knock sensor and may retard the ignition timing. This ignition timing is learned by the ECM and placed in memory. NOTE: This area of memory can not be viewed by using the Select Monitor. When the vehicle is driven uinder these conditions, the timing may be retarded and could cause the engine to hesitate on acceleration. To confirm this condition, road test the vehicle while viewing the Knock Sensor Signal on the Select Monitor. If you duplicate the hesitation, and the reading on the monitor is around -10 degrees, you will need to change the ECM to correct the concern. [note: this is an enhanced ECM, not a replacement with the same component]
Sometimes the engine will cut out very briefly right as I press the gas pedal. This Subaru service bulletin explains what can cause this problem:
HESITATION ON ACCELERATION - 11-53-98 (2/99)
Applicability: 97-98 Legacy, Impreza, and Forester Manual Transmission Vehicles with 2.5l and 2.2l engines.
In the event you encounter a customer complaint of a slight engine hesitation between 1500-2500 rpm's when the engine is cold or hot, perform the following
Eliminate all external influences, such as an incorrect or dirty air filter, loose or tracked intake duct, dirty fuel filter, low fuel pressure, PVC system, or low engine vacuum that would indicate an external leak or an internal engine component.
If all external components are confirmed to be operating within vehicle specifications, the hesitation may be caused by the ignition control logic in the ECM. Under certain low rpm driving patterns, the ignition control system can pick up engine vibrations through the knock sensor and may retard the ignition timing. This ignition timing is learned by the ECM and placed in memory. NOTE: This area of memory can not be viewed by using the Select Monitor. When the vehicle is driven uinder these conditions, the timing may be retarded and could cause the engine to hesitate on acceleration. To confirm this condition, road test the vehicle while viewing the Knock Sensor Signal on the Select Monitor. If you duplicate the hesitation, and the reading on the monitor is around -10 degrees, you will need to change the ECM to correct the concern. [note: this is an enhanced ECM, not a replacement with the same component]
- Mike W., South Hero, VT, US