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1F – 376 ENGINE CONTROLS
ROUGH, UNSTABLE, OR INCORRECT IDLE, STALLING
Definition: The engine runs unevenly at idle. If the condi-
tion is bad enough, the vehicle may shake. Also, the idle
varies in rpm (called "hunting"). Either condition may be
severe enough to cause stalling. The engine idles at in-
correct idle speed.
Step
Were the Important Preliminary Checks performed?
1
1. Connect the scan tool to the Data Link Connector
(DLC).
2. Monitor the pre-converter oxygen sensor (O2S 1)
2
reading at different throttle positions.
Does the O2S 1 sensor change quickly from rich to
lean at the different throttle positions?
Check the O2S 1 for contamination from fuel or
improper use of RTV sealant.
3
Is the O2S 1 contaminated?
Replace the contaminated O2S 1 as needed.
4
Is the repair complete?
1. Check for a sticking throttle shaft or binding
throttle linkage that may cause incorrect Throttle
Position (TP) sensor voltage.
5
2. Check the TP sensor voltage reading with the
throttle closed.
Is the TP sensor voltage within the value specified?
1. Check the Engine Coolant Temperature (ECT)
sensor voltage reading using the scan tool.
2. Compare the ECT reading with the ambient
6
temperature when the engine is cold.
Does the ECT reading differ from the ambient
temperature by more than the value specified?
Check for high resistance in the ECT circuit or the
sensor itself.
7
Is the problem found?
Replace the ECT or repair the circuit as needed.
8
Is the repair complete?
Check the Manifold Absolute Pressure (MAP)
sensor for response and accuracy.
9
Is the problem found?
Replace the MAP sensor or repair the MAP sensor
circuit as needed.
10
Is the repair complete?
1. Road test the vehicle at the speed of the
complaint.
11
2. Monitor the fuel trim reading using the scan tool.
Is the fuel trim reading within the value specified?
Is the fuel trim reading below the value specified?
12
Action
Important: Before diagnosing the symptom, check ser-
vice bulletins for updates.
Value(s)
–
Go to Step 2
–
Go to Step 5
–
Go to Step 4
–
System OK
0.4-0.8 v
Go to Step 6
3_C (5_F)
Go to Step 7
–
Go to Step 8
–
System OK
–
Go to Step 10
–
System OK
–20%~25%
Go to Step 14
"Diagnostic Aids
–20%
for DTC P0171"
Yes
No
Go to
"Important
Preliminary
Checks"
Go to Step 3
Go to Step 5
–
Go to
"Diagnostic
Aids for
DTC P0123"
Go to Step 9
Go to Step 9
–
Go to Step 11
–
Go to Step 12
Go to
Go to Step 13
DAEWOO T-154 BL2,3
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