Running rough and rich at idle

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95slowhoe

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Ok so now the tahoe's symptoms have changed. When its cold it runs smooth and dosen't miss a beat. But when it gets up to operating temp it starts to misfire and run rough.
 

SunlitComet

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Have you disconnected the battery after you did this. I am thinking it might be stuck in an a limp mode becuase it has not recognized yet the glitches may be gone. it can take several trips to do it on it's own but the battery disconnect would be quicker.When it does get up to temp it does switch to closed loop mode. If you clear out it's memory and it still acts up can you try pulling codes again with a hot engine and maybe pick up something in closed loop. I find it unusual the it is not telling you itself first thru MIL illumination.
 
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95slowhoe

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I did disconnect the battery when I put the new iac in. And I have put around 50 miles on it since then. It still runs rough but only when it gets warmed up, now that I replaced the iac. And know cel has come on yet.
 

SunlitComet

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Not sure if this will help but will pass it along:

Also just in cas edo you want some info for testing the coolant temp sensor for computer? You just need a multimeter.

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: Flow of Diagnosis\Diagnostic Notes

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 driveability 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: Diagnostic Trouble Code Tests and Associated Procedures\Manufacturer Code Charts\DTC 15\Powertrain Controls - ECM/PCM
* MAP sensor response and accuracy - Refer to "Manifold Absolute Pressure (MAP) Output Check." See: 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: 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: 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: Diagnostic Trouble Code Tests and Associated Procedures\Related Tests and Information\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: 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.
 
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95slowhoe

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Ok well I found out what was wrong finally. My timing was about 10° advanced. Set it to 0° and all is good now. Thanks for all your help sunlitcomet.
 

SunlitComet

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Make sure you set it using this method:


* Engage the parking brake and block the wheels.
* Place the transmission in neutral.

1. Refer to the Vehicle Emissions Control Information label under the hood. Always follow the Vehicle Emissions Control Information label procedures first before using the following procedure.
2. Put the IC system in the bypass mode by disconnecting the "set timing" connector. This is a single wire sealed connector that has a tan with black stripe lead. This connector breaks out of the wiring harness below the heater case in the passenger compartment.
3. With the ignition switch "OFF," connect the pickup lead of the timing light to the number one spark plug. Use a jumper lead between the wire and plug or an inductive type pickup. DO NOT pierce the wire or attempt to insert a wire between the boot and the wire. Connect the timing light power leads according to manufacturer's instructions.
4. Start the engine, and aim the timing light at the timing mark. The line on the balancer or pulley will line up at the timing mark. The timing should be O°TDC . If a change is necessary, loosen the distributor hold-down clamp bolt at the base of the distributor. While observing the mark with the timing light, slightly rotate the distributor until the line indicates the correct timing. Tighten the hold-down bolt, and recheck the timing.
5. Turn "OFF" the engine and remove the timing light. Reconnect the number one spark plug wire, if removed.
6. Reconnect the "Set Timing" connector.

:Handshake:
 

gulleyman

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Glad you got yours solved! Looks like mine may be a bad valve or head :(
 

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