Document ID# 204377
1998 Oldsmobile Achieva

Hesitation, Sag, Stumble

Definition: Momentary lack of response as the accelerator is pushed down.
Can occur at any vehicle speed. Usually more pronounced when first trying to
make the vehicle move, as from a stop sign. May cause the engine to stall if
severe enough.

Preliminary
. Refer to Powertrain On Board Diagnostic (OBD) System Check .
. Refer to Symptoms .
. Search for service bulletins.

Sensor/System
. Check the oxygen sensor (O2S 1). The O2S 1 and HO2S 2 should respond
quickly to different throttle positions. If not, check the O2S 1 for silicon
or other contaminants from fuel or the use of improper RTV sealant. The
sensor may have a white powdery coating. Silicon contamination causes a high
but false O2S 1 signal voltage (rich exhaust indication). The PCM will
reduce the amount of fuel delivered to the engine, causing a severe
driveability problem. Refer to oxygen sensor in Information Sensors/Switches
Description .
. Check the EGR valve for a stuck open pintle.
. Check for proper operation of the MAP Sensor.
. Check for proper operation of the TP sensor.
. Check for proper operation of the ECT sensor.

Fuel System
. Check the fuel pressure. Refer to Fuel System Diagnosis .
. Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel
Diagnosis .
. Check the injectors. Refer to Fuel Injector Balance Test .
. Check items which can cause an engine to run rich (long term fuel trim is
significantly in the negative range). Refer to DTC P0172 Fuel Trim System
Rich .
. Check items that can cause an engine to run lean (long term fuel trim is
significantly in the positive range). Refer to DTC P0171 Fuel Trim System
Lean .
. Check for proper operation of the evaporative emission (EVAP) control
system.

Ignition System
. Check for proper ignition voltage output with the spark plug jumper wires
J 36012-A and spark tester J 26792 .
. Check the spark plugs for the following conditions:
. Wet or fuel fouled spark plugs
. Cracks on the spark plugs
. Wear
. Improper spark plug gap
. Burned electrodes or heavy deposits
. If the spark plugs are fuel or oil fouled, the cause of the fouling must
be determined before replacing the spark plugs.
. Check the ignition control module (ICM) for proper ground connection.
. Check the ignition coils for cracks or carbon tracking.

Additional Checks
. Check for proper operation of the Automatic Transaxle.
. Check the generator output voltage. Repair the generator if the output
voltage is less than 11 volts or more than 16 volts.
. If all procedures have been completed and no malfunctions have not been
found, review and inspect the following items:
. Visually and physically inspect all electrical connections within the
suspected circuit and/or systems.
. Check scan tool data.