Code
P1124
DAEWOO
P — Powertrain
IDLE RATIO (IDLING)-LEAN
AI status
Completed
Completed
100%
Causes
- Intake vacuum leak (hose, gasket, manifold)
- Faulty or dirty mass airflow (MAF) or manifold absolute pressure (MAP) sensor
- Low fuel pressure (weak pump, clogged filter, faulty regulator)
- Partially blocked or leaking fuel injectors
- Stuck-open EGR valve or excessive EGR flow at idle
- Faulty or slow idle air control (IAC) / throttle body contamination
Symptoms
- Rough or high/low unstable idle; engine may stall at idle
- Check Engine Light (MIL) set with P1124 stored
- Hesitation or stumble on acceleration from idle
- Increased crank time or hard starting when hot or cold
- Possibly reduced fuel economy or misfire codes if severe
What to check
- Retrieve freeze-frame and all stored DTCs with a scan tool; note engine conditions at fault
- Visually inspect intake tract, vacuum hoses, PCV line, and intake manifold gaskets for leaks or damage
- Smoke test intake system to find hidden vacuum leaks
- Monitor live data at idle: STFT/LTFT, MAF (g/s or V), MAP (kPa), O2 sensor voltages/trim response, IAC position
- Measure fuel pressure at rail and compare to specification
- Inspect and clean throttle body and IAC/idle control passages
Signal parameters
- Short-term fuel trim (STFT) and long-term fuel trim (LTFT) at idle
- MAF sensor reading (g/s or V) at idle and when revved
- MAP pressure (kPa) / vacuum at idle
- O2 sensor voltage and switching frequency (narrowband) or reported lambda (wideband)
- Fuel rail pressure (psi / bar) at idle and during cranking
- Idle Air Control (IAC) commanded and actual position
Diagnostic algorithm
- Connect a scan tool, record freeze-frame data and all related DTCs. Do not assume P1124 is the only issue.
- Visually inspect intake plumbing, vacuum hoses, PCV, and throttle body for obvious leaks or disconnections.
- Perform an intake smoke test to locate small vacuum leaks; repair any leaks found and clear codes.
- With scan tool, monitor STFT/LTFT at idle. Significant positive trims (+10% or more) indicate a lean condition; correlate to MAF/MAP readings.
- Check fuel pressure at the rail under static and cranking conditions; compare to manufacturer spec. Repair fuel delivery if low.
- Inspect/clean throttle body and IAC passages; verify IAC response and commanded idle steps. Replace if inoperative.
- Test MAF and MAP sensors: clean MAF if contaminated, verify MAP voltage/pressure response. Replace if out of specification.
- Check O2 sensor operation (voltage swings or lambda) to ensure closed-loop feedback is functioning. Replace slow or failed sensors.
- If injectors are suspected, perform injector balance or flow testing and clean/replace as needed.
- Inspect EGR/PCV systems for sticking or excessive flow at idle and repair as required.
- Repair identified faults, clear codes, and retest under the same conditions that set the code to confirm resolution.
Likely causes
- Undetected intake vacuum leak around throttle body or manifold
- Contaminated/throttled throttle body or IAC valve restricting proper idle air control
- Weak fuel pressure due to failing pump or clogged filter
- MAF or MAP providing incorrect airflow data (dirty or failed)
- Open or leaking PCV/EGR system allowing excess air into intake
- O2 sensor slow to respond or out of range at idle skewing fuel trims
Fault status
Status
PCM detected a lean condition during idling (too much air or too little fuel). The MIL is stored and relevant freeze-frame data recorded; further diagnosis required to find source of excess air or insufficient fueling.
Repair difficulty: Medium
Diagnostic time: 1.5 - 3.0 hours
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Repair manuals
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75
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