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  1. #1
    Newbie
    Join Date
    Sep 2011
    Location
    Spokane, Washington, United States
    Posts
    8

    Default Idle is very low

    When my truck is all warmed up and and I go for a drive in it (like work or run errons) the idle is very low when I come up to a stoplight .. It's around 100-200 rpm. In the mornings when I first start it it idles fine where it's suppose to when it's cold out .. Same when it in "park" it idles fine.. Only when it's in drive and I'm at a complete stop it's way too low.. It also feels like a stutter in the engine because of how low the idle is .. ... Is there a way I can adjust this or get it fixed?????

    1994 Chevy silverado z71
    5.7 liter 350
    Automatic transmission

  2. #2

    Default

    Hello Mario, just posted this to another users issue. Seems to be similar to his so I will post the same info.
    Hope this helps.

    1995 GMC Truck C 2500 P/U 2WD V8-350 5.7L VIN K TBI
    Fuel Delivery and Air Induction: Testing and Inspection Procedures
    Hesitation, Sag or Stumble
    SYMPTOM DEFINITION:
    Momentary lack of response as the accelerator is pushed down. Can occur at any vehicle speed. Usually most severe when first trying to make
    the vehicle move, as from a stop sign. May cause the engine to stall if severe enough.
    PRELIMINARY CHECKS
    -Refer to Diagnostic Notes. See: Computers and Control Systems/Testing and Inspection/Symptom Related Diagnostic Procedures/A

    Diagnosis by Symptom
    FUEL SYSTEM
    Check:
    -Fuel pressure.

    -Throttle Position
    (TP)
    sensor Check TP sensor for binding or sticking. Voltage should increase at a steady rate as throttle is moved toward Wide Open Throttle (WOT).

    -MAP sensor response and accuracy. Refer to "Manifold Absolute Pressure
    (MAP)
    Output Check." See: Computers and Control
    Systems/Testing and Inspection/Component Tests and General Diagnostics/Manifold Absolute Pressure (MAP) Output Check

    -Water/contaminated fuel.
    -Canister purge system for proper operation.

    IGNITION SYSTEM
    Check:
    -Spark plug wires for being faulty.
    -Spark plugs for being fouled.
    -Open ignition system ground CKT 453 or ignition timing.

    ADDITIONAL CHECKS
    Check:
    -Service Bulletins for PROM updates.
    -Generator output voltage. Repair if less than 9 or more than 16 volts.
    -EGR valve operation.







    1995 GMC Truck C 2500 P/U 2WD V8-350 5.7L VIN K TBI

    Fuel Delivery and Air Induction: Testing and Inspection Procedures
    Rough, Unstable or Incorrect Idle, Stalling
    SYMPTOM DEFINITION:
    The engine runs unevenly at idle. If bad enough, the vehicle may shake. Also, the idle may vary in rpm (called "hunting"). Either condition may
    be severe enough to cause stalling. Engine idles at incorrect speed.
    PRELIMINARY CHECKS
    -Refer to Diagnostic Notes. See: Computers and Control Systems/Testing and Inspection/Symptom Related Diagnostic Procedures/A

    Diagnosis by Symptom
    SENSORS
    Check:
    -Oxygen Sensor
    (O2S)
    - Inspect sensor for silicon contamination from fuel, or use of improper sealant (never use sealant on any waterproof connectors). The sensor will have a white, powdery coating, and will result in a high but false signal voltage (rich exhaust indication). The control module will then reduce the amount of fuel delivered to the engine, causing a severe drivability problem.

    -Throttle Position
    (TP)
    sensor - If a sticking throttle shaft or binding linkage causes a high TP sensor voltage open throttle indication, the control module will not control idle. Monitor TP sensor voltage. A scan tool and/or voltmeter should read less than 0.85 volt with throttle closed.

    -Engine Coolant Temperature
    (ECT)
    sensor - Using a scan tool, compare engine coolant temperature with ambient temperature on a cold
    engine.
    -If engine coolant temperature reads 5 degrees greater than or less than ambient air temperature. Check for high resistance in coolant sensor circuit or sensor itself. Refer to "DTC 15 Diagnostic Aids." See: Computers and Control Systems/Testing and Inspection/Diagnostic Trouble Code Tests and Associated Procedures/Manufacturer Code Charts/DTC 15/Power train Controls -ECM/PCM

    -MAP sensor response and accuracy - Refer to "Manifold Absolute Pressure
    (MAP)
    Output Check." See: Computers and Control
    Systems/Testing and Inspection/Component Tests and General Diagnostics/Manifold Absolute Pressure (MAP) Output Check

    FUEL SYSTEM
    Check:
    -To determine if the condition is caused by a rich or lean system, the vehicle should be driven at the speed of the complaint. Monitoring fuel trim will help identify problem.
    -Lean - Long term fuel trim greater than 150. Refer to "DTC 44 Diagnostic Aids." See: Computers and Control Systems/Testing and Inspection/Diagnostic Trouble Code Tests and Associated Procedures/Manufacturer Code Charts/DTC 44/Powertrain Controls - ECM/PCM
    -Rich - Long term fuel trim less than 115. Refer to "DTC 45 Diagnostic Aids." See: Computers and Control Systems/Testing and Inspection/Diagnostic Trouble Code Tests and Associated Procedures/Manufacturer Code Charts/DTC 45/Powertrain Controls - ECM/PCM

    -Evaporative emission control system.
    -Perform a cylinder compression check.
    -For injector(s) leaking. Check fuel pressure. Refer to "Chart A-6." See: Computers and Control Systems/Testing and Inspection/Symptom Related Diagnostic Procedures/A - E Charts & Related Test Procedures/Chart A-6 Fuel System Diagnosis
    -Idle speed actuator operation.

    IGNITION SYSTEM
    Check:
    -Ignition system and ignition timing.
    ADDITIONAL CHECKS
    Check:
    -Vacuum leaks can cause higher than normal idle and low IAC counts.
    -IAC operation - refer to "DTC 35." See: Computers and Control Systems/Testing and Inspection/Diagnostic Trouble Code Tests and Associated Procedures/Manufacturer Code Charts/DTC 35/Powertrain Controls - ECM/PCM -Control module grounds for clean, tight, and proper routing.

    -Trans Range
    (TR)
    pressure switch assembly operation.
    -Use scan tool to determine if control module is receiving A/C signal. If problem exists with A/C "ON," check A/C system operation.
    -EGR "ON," while idling, will cause roughness, stalling and hard starting.
    -Battery cables and ground straps should be clean and secure. Erratic voltage will cause IAC to change its position, resulting in poor idle
    quality.

    -IAC valve will not move if system voltage is below 9 or greater than 16 volts.
    -A/C refrigerant pressure too high or faulty high pressure switch.
    -Crankcase ventilation valve for proper operation by placing finger over inlet hole in valve end several times. Valve should snap back. If not, replace valve.

    ENGINE MECHANICAL
    Check:
    -For broken motor mounts or low compression.

  3. #3

    Default

    if its acting funny and act like its going to die, might be a vacuum tube
    1994 Silverado Z71 1500 4x4
    BF Goodrich 31in All-Terrain Tires
    Painted frame-arms-axle
    Blazer Fog lights
    Removed front splash guard
    Tow hook Chains
    Locking gas cap
    REFLEXXION Rear bumper (Painted black)
    Diamond metal bed caps & Truck Box
    Painted engine bay
    Vinyl Flooring
    Bed insert
    Blistein Shock absorbers
    BOSS bluetooth LCD Radio
    Platinum trucker CB antenna
    Midland 5001z CB Radio
    XO backup camera
    X-press Remote entry-alarm
    CUSTOM metal gas & brake pedal
    Highland fold-away bed cleats
    Race thermostat

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