Idle problem on a 2006 chevy trailblazer 4.2

Clean out the throttle body and reset the code.

Take it back and tell the repair shop that they need to correct the issues that are not right.

clean the throttle plate. this is not a vacuum leak concern. a vacuum leak would cause higher idle and lean codes

DTC P0506

CIRCUIT DESCRIPTION
The throttle actuator control (TAC) motor is controlled by the engine control module (ECM). The DC motor located in the throttle body drives the throttle plate. In order to decrease idle speed, the ECM commands the throttle closed reducing air flow into the engine and the idle speed decreases. In order to increase idle speed, the ECM commands the throttle plate open allowing more air to pass the throttle plate. If the actual idle RPM does not match the desired idle RPM within a calibrated time, this DTC sets.

DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC P0506 Idle Speed Low

CONDITIONS FOR RUNNING THE DTC
- DTCs P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0122, P0123, P0171, P0172, P0201, P0202, P0203, P0204, P0205, P0206, P0207, P0208, P0220, P0121, P0222, P0223, P0230, P0300, P0336, P0442, P0446, P0449, P0452, P0453, P0455, P0462, P0463, P0496, P1516, P2101, P2135, P2176 are not set.
- The engine is operating for at least 60 seconds.
- The engine coolant temperature (ECT) is more than -60°C (-140°F).
- The intake air temperature (IAT) is more than -10°C (-14°F).
- The barometric pressure (BARO) is more than 65 kPa.
- The system voltage is between 9-18 volts.
- The vehicle speed is less than 1.6 km/h (1 mph).
- DTC P0506 runs continuously when the above conditions are met.

CONDITIONS FOR SETTING THE DTC
- The actual idle speed is approximately 100 RPM lower than the desired idle speed.
- The above condition is present for 5 seconds.

ACTION TAKEN WHEN THE DTC SETS
- The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
- The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
- The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
- Clear the MIL and the DTC with a scan tool.

TEST DESCRIPTION

View & Print Options Step 1 - Step 5
The number below refers to the step number on the diagnostic table.
2. This test determines whether the engine can achieve the commanded RPM. If the engine does not reach the commanded RPMs, the test determines whether the RPM is too high or too low.
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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 )

DTC P0506 refers to the actual engine idle speed not being within range of the commanded engine idle speed. If there are any other DTCs present those must be fixed first.

This can be caused by an ISC (Idle Speed Control) motor sticking.

Other possible causes of this code are:
- incorrect TCC (Torque Converter Clutch) operation
-accessories that require additional engine torque to operate - including amplifiers, security systems, etc. that can cause additional electrical load.
- Restricted exhaust system
-any other mechanical problem that may affect engine speed.

P0506 - Idle Air Control (IAC) System RPM Lower Than Expected

What does that mean?
This P0506 code is one that's sometimes triggered on vehicles that have electronic throttle control. That is, they don't have a regular throttle cable from the accelerator pedal to the engine. They rely on sensors and electronics to control the throttle. In this case, the P0506 DTC (diagnostic trouble code) is triggered when the PCM (powertrain control module) detects an engine idle speed that is lower than the desired (pre-programmed) RPM.

Potential Symptoms: Most likely the only thing you'll notice is the idle speed is lower than normal so it will likely be rougher. There are potentially other symptoms as well. Of course, when trouble codes are set, the MIL (malfunction indicator lamp, a.k.a. the check engine light) illuminates.

Causes: A P0506 DTC trouble code may be caused by one or more of the following:
* A vacuum leak
* An air restriction in the intake air path or exhuast
* A faulty positive crankcase ventilation (PCV) valve
* Damaged/failed/dirty throttle body
* Internal engine problem
* Failed PCM

Possible Solutions:
This DTC is more of an informational code, so if there are any other codes set, diagnose them first. If there are no other codes, inspect for vacuum leaks, restrictions, and damage. If there are no symptoms other than the DTC itself, just clear the code and see whether it returns.

Other related DTCs: P0507

P0506 - Idle Air Control (IAC) System RPM Lower Than Expected

What does that mean?
This P0506 code is one that's sometimes triggered on vehicles that have electronic throttle control. That is, they don't have a regular throttle cable from the accelerator pedal to the engine. They rely on sensors and electronics to control the throttle. In this case, the P0506 DTC (diagnostic trouble code) is triggered when the PCM (powertrain control module) detects an engine idle speed that is lower than the desired (pre-programmed) RPM.

Potential Symptoms
Most likely the only thing you'll notice is the idle speed is lower than normal so it will likely be rougher. There are potentially other symptoms as well. Of course, when trouble codes are set, the MIL (malfunction indicator lamp, a.k.a. the check engine light) illuminates.

Causes
A P0506 DTC trouble code may be caused by one or more of the following:
* A vacuum leak
* An air restriction in the intake air path or exhuast
* A faulty positive crankcase ventilation (PCV) valve
* Damaged/failed/dirty throttle body
* Internal engine problem
* Failed PCM

Possible Solutions
This DTC is more of an informational code, so if there are any other codes set, diagnose them first. If there are no other codes, inspect for vacuum leaks, restrictions, and damage. If there are no symptoms other than the DTC itself, just clear the code and see whether it returns.

idle control rmp low check air filter pcv valve and fuel pressure from fuel pump

This P0506 code is one that's sometimes triggered on vehicles that have electronic throttle control. That is, they don't have a regular throttle cable from the accelerator pedal to the engine. They rely on sensors and electronics to control the throttle. In this case, the P0506 DTC is triggered when the PCM detects an engine idle speed that is lower than the desired (pre-programmed) RPM.

Most likely the only thing you'll notice is the idle speed is lower than normal so it will likely be rougher. There are potentially other symptoms as well. Of course, when trouble codes are set, the MIL illuminates. Such as the P0300 which is an indication of multiple misfires to the spark plugs. 

A P0506 DTC trouble code may be caused by one or more of the following:

• A vacuum leak 
• An air restriction in the intake air path or exhaust
  
• A faulty positive crankcase ventilation (PCV) valve
  
• Damaged/failed/dirty throttle body
  
• Internal engine problem
  
• Failed PCM
  

Hope this helps, keep me posted if you have any more questions. Be glad to help you get your blazer running 100% again.