2003 impala intermittent high idle with high iac count iac tested good

That could be a lot of thing's , stalling when ,cold ,hot ,idling , in gear , coming to a stop etc... Could have a vacuum leak , problem with IAC valve - idle air control , an one of a few different sensors could be bad , mass air flow sensor , coolant temp sensor etc.. You need to have some testing done , scan tool hooked up to check for DTC'S - diagnostic trouble codes , also check engine sensor data parameters . What engine does yours have ? 3.4 or 3.8 L .
Sensor/System
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Test for conditions which cause an incorrect idle speed.

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Throttle body tampering, excessive deposits, or damage. Refer to Fuel System Description .

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Restricted air intake system

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Large vacuum leak

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Inspect the air intake ducts for being collapsed, damaged areas, looseness, improper installation, or leaking especially between the mass air flow (MAF) sensor and the throttle body.

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Inspect crankcase ventilation valve for proper operation.

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Inspect the throttle position (TP) sensor and related wiring. Refer to DTC P0123 .

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Monitor the 24X crank sensor and the CMP sensor present parameters on the scan tool. If both are not responding, test the sensor feed circuit. Both sensors use a separate feed circuit but are internally connected to power. Test all CKP sensor A and CMP sensor circuits for intermittents. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

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Monitor the 3X parameter on the scan tool. If the 3X is not responding, inspect the CKP sensor B and circuits for intermittents. Inspect the ignition control (IC) circuit, IC timing control circuit, low resolution engine speed signal circuit and the low reference circuit for intermittents. If these circuits become open, or shorted may not set a DTC immediately, but are capable of causing driveability complaints. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

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Test the exhaust gas recirculation (EGR) system for proper operation. Refer to Exhaust Gas Recirculation (EGR) System Description .

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Inspect the transaxle range switch input with the vehicle in drive and the gear selector in drive or overdrive.

Here are some tests you can try. The list is generic and you may have tried some of these already. It sounds like a vacuum line issue to me. For other info try this website:

Repair Guides Symptom Diagnosis no Codes What To Do When There Are No...

Preliminary Checks
Prior to starting this symptom test routine, inspect these underhood items:

1. All related vacuum lines for proper routing and integrity.
2. All related electrical connectors and wiring harnesses for faults (Wiggle Test).
3. Check the throttle linkage for a sticking or binding condition.
4. Air Intake system for restrictions (air inlet tubes, dirty air filter, etc.).
5. Search for any technical service bulletins related to this symptom.
6. Turn the key to off. Unplug the MAP sensor connection and restart the engine to recheck for the idle concern. If the condition is gone, replace the MAP sensor.

Test 2: Rough, Low or High Idle Speed Condition (Continued)
Test 2 Chart
Step Action Yes No 1 Step Description: Verify the rough idle or stall Does the engine have a warm engine rough idle, low idle or high idle condition in P or N- Go to Step 2. Fault is intermittent. Return to the Symptom List and select another fault. 2 Step Description: Verify idle speed & timing Verify the base timing is within specifications Verify that the base idle speed is set properly Are the timing and idle speed set properly- Go to Step 3. Set the base idle speed and timing to the specifications and then retest for the symptom. 3 Step Description: Check AIS / IAC Operation Check the AIS or IAC motor operation Inspect the AIS/IAC housing in throttle body for restricted passages. Clean as needed. Set the parking brake, block the drive wheels and turn the A/C off. Install the Scan Tool. IAC Motor Tester - Turn the key off and then connect the IAC tester to the IAC valve. Start the engine and use the IAC tester to extend and retract the IAC valve. ATM Test - Start the engine. Use the tool to change the speed from min-idle to 1500 rpm. Did the idle speed change as commanded- Install an Aftermarket Noid light and check the operation of the PCM and AIS or IAC motor circuits. Check the motor for signs of open or shorted circuits. Replace the IAC motor or PCM as needed or make repairs to the IAC motor wiring. If all are okay, go to Step 4. If the AIS/IAC motor passages are clean and engine speed did not change as described when the AIS/IAC motor was extended and retracted, replace the AIS/IAC motor. Then retest for the condition. 4 Step Description: Check/compare PID values Connect Scan Tool & turn off all accessories. Start the engine and allow it to fully warmup. Monitor all related PIDs on the Scan Tool. Verify the P/N switch input in gear and Park. Check the O2S operation with a Lab Scope. Are all PIDs within normal range- Go to Step 5. Note: An IAC motor count of over 80 indicates the pintle is extended and an IAC count of (0) indicates the pintle is retracted. One or more of the PIDs are out of range when compared to "known good" values. Make repairs to the system that is out of range, then retest for the symptom. 5 Step Description: Check the Ignition System Inspect the coils for signs of spark leakage at coil towers or primary connections. Check the spark output with a spark tester. Test Ignition system with an engine analyzer. Were any faults found in the Ignition system- Make repairs as needed Go to Step 6. 6 Step Description: Check the Fuel System Inspect the Fuel delivery system for leaks. Test the fuel pressure, quality and volume. Test the operation of the pressure regulator. Were any faults found in the Fuel system- Make repairs as needed Go to Step 7. 7 Step Description: Check the Exhaust System Check Exhaust system for leaks or damage. Check the Exhaust system for a restriction using the Vacuum or Pressure Gauge Test (e.g., exhaust backpressure reading should not exceed 1.5 psi at cruise speeds). Were any faults found in Exhaust System- Make repairs to the Exhaust system. Then retest the symptom. Go to Step 8. Repair Guides Symptom Diagnosis no Codes What To Do When There Are No...

Check in side by throttle body if spring is coming back if OK,could be TPS sensor or IAC.

Before change computer #1 TPS sensor # 2 IAC sensor,that you should change first.

Good to hear from you. Nice work.

code P0128 ECT ( electronic coolant temperature ) engine temperature to low ( replace thermostat ).

code P0300 engine miss fire detected ( replace spark plugs and spark plug wires )

code P0506 IAC ( idle air control ) system idle to low ( clean the IAC valve if problem persists replace the IAC valve )

To me it sounds like the (fuel pressure valve) located on the end of the fuel rail, by the throttle body, also check vacuum line.

123 throttle position sensor/switch A circuit high input 121 throttle position sensor/switch A circuit range/performance problem if running fine try reset--- if running rough black smoke star problems check the TPS wiring ,connections,and mounting if looks good not grounding ,rubbing or damage to wiring than test TPS sensor

A code P0123 may mean that one or more of the following has happened:

• TPS not mounted securely
• TPS circuit short to ground or another wire
• Faulty TPS
• Damaged computer (PCM)

Possible Solutions If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.
If there are symptoms such as the engine is stumbling or hesitating, carefully inspect all wiring and connectors that lead to the TPS. More than likely the problem is with the TPS wiring. Check the voltage at the TPS (refer to a service manual for your vehicle for this specific information). If the voltage spikes or is too high (over 4.65 volts with key on, engine off), then that is indicative of a problem. Carefully trace each wire from the TPS wiring harness to check for breaks, rubbing against other components, etc.
A code P0121 may mean that one or more of the following has happened:

• TPS has intermittent open or short internally
• Harness is rubbing and causing an open or short in the wiring
• Bad connection at the TPS
• Bad PCM (less likely)
• Water or corrosion in connector or sensor

Possible Solutions 1. If you have access to a scan tool, see what the idle and WOT (wide open throttle) readings are for the TPS. Check if they're close to the specifications mentioned above. If not, then replace the TPS and re-check.
2. Check for an intermittent open or short in the TPS signal. To do that, you can't use a scan tool. You'll need an oscilliscope. The reason is because scan tools take samplings of many different readings over just one or two data lines and can miss an intermittent drop out. Hook up your oscilliscope and watch the signal. It should sweep up and down smoothly with no drop outs or spikes.
3. If no problems were noticed, perform a wiggle test. Do this by wiggling the connector and harness while watching the pattern. Does it drop out? If so, replace TPS and re-check.
4. If you have no TPS signal, check for 5 Volt reference at the connector. If it's present, check the ground circuit for open or shorts.
5. Make sure the signal circuit isn't 12V. It should never have battery voltage. If it does, trace circuit for short to voltage and repair.
6. Look for any water in the connector and replace TPS as necessary.
P0152 Oxygen Sensor Circuit High Voltage (Bank 2 Sensor 1)

massair frow sensor