Re: engine is revved up like the throttle is stuck and...
Idle air control sesnor could also be the culprit . If so its not real hard to find sits on the plenum its probably black or silver in color . When the go out it can cause it to not idle at all or wide open.Shouldn,t be that exspensive as far as the part is concerned i'd say around 50 or 60 maybe .Hope this helps
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I am not too familiar with Australian vehicles, except the rebadged Holden Monero that was sold as a "Pontiac GTO" in the States in 2005 and 2006, and since your Holden is likely to be a GM vehicle, I am sure the same diagnosis applies. You have what is called an Idle Air Control valve that is located on the throttle body. If it is stuck in the wide open position, it will cause your engine to race. I would say that is the first place to look. GM has a huge problem with their IAC valves going bad.
It could be a number of things but I would start by using a diagnostic device in order to determine exactly what the vehicles ECU has to report.
Based on your description I would look at the throttle position sensor.
Irregular revving of the engine could be pin pointed to the idle control valve, but only if the revving is relatively small.
If it seems like someone has their foot on the accelerator, and has it planted firmly to the floor, then I would definitely be looking at the idle throttle position sensor.
Some vehicles also use a fly by wire system where the accelerator cable goes to a throttle position sensor that isn't even near the engine.
It can be located under the battery tray sometimes and can be quite easy to get to.
These types of sensors are relatively cheap to replace but are quite common in their failure rate.
All being said, I would definitely recommend you use a diagnostic device first.
It will not only save you time, it will also narrow down the fault more precisely.
Some throttle position sensors are adjustable. Follow manufacturer's instructions.
On older engines, correct adjustment is crucial to proper system operation.
On newer engines, this is not as important because the computer uses whatever reading it takes at idle as base voltage (adaptive learn strategy).
Incorrect TP sensor adjustment may cause:
Inaccurate idle speed,
Engine stalling, and
Follow these steps to adjust a typical TP sensor:
Backprobe the TP sensor signal wire and connect a voltmeter from this wire to ground.
Turn on the ignition switch and observe the voltmeter reading with the throttle in the idle position.
If the TP sensor does not provide the specified voltage, loosen the TP sensor mounting bolts and rotate the sensor housing until the specified voltage is indicated on the voltmeter.
A TP Sensor with elongated slots for sensor adjustments. Courtesy of General Motors Corporation - Chevrolet Motor Division.
Hold the sensor in this position and tighten the mounting bolts to the specified torque.
Most throttle position sensors are made so that their adjustments are tamperproof. They have screws that are either soldered or staked.
To remove the switch, these might need to be drilled or filed off. After the new switch is installed and adjusted, the new mounting screws are restaked.
replacing these items won`t cause your problem.you will have to find out what code set the light and go from there.you don`t say if the revving is at idle or not if it is you could have a bad idle control motor or a cracked vacuum hose that acts up at certain times.even a bad throttle position sensor(tps),egr valve,so its important to know what set the light on.
Idle Speed Control (ISC) Motor OPERATION Eagle Throttle Body Fuel Injection (TBI) System NOTE: The Eagle TBI system is used only on 2.5L Premier engines.
The Idle Speed Control (ISC) motor is mounted to the throttle body and controlled by the PCM. The throttle lever rests against the initial adjustment screw of the actuator (plunger). The idle speed is not adjustable. The initial adjustment screw is only used to establish the initial positioning of the actuator when the ISC motor has been replaced.
The actuator extends or retracts to control engine idle speed and to set throttle stop angle during deceleration. Based on inputs from the various engine control system sensors and switches to the PCM supplies current to the ISC motor to adjust the actuator position for the particular operating conditions.
Depending on whether your car is Injected or Carby induction, The aircon system has an IDLE UP circuit which is supposed to raise the Idle while the Aircon Compressor is engaged. The Compressor cycles on & off to charge the system pressure as required. The Idle up system typically uses an IDLE UP SOLENOID which is usually mounted directly on the throttle linkage at the Carby or Throttle body itself, or a Vacuum Solenoid which switches vacuum to a Diaphram which is connected to a linkage on the Carby or Throttle body itself, or a Vacuum Switch which ports air into the throttle body to raise idle (This type on injected vehicles only). It sounds as if the IDLE UP system has failed or is not adjusted properly. Revving the engine spins the compressor faster thus charging the system sufficiently to dis-engage the compressor, which in turn removes the load from the engine, allowing it to idle again. A simple way to test is to disconnect the Aircon clutch wire (make sure it cannot fall into belt) & switch on the Air with the engine running. The RPM should raise typically around 300 RPM. If it doesn't the IDLE UP is not working. Hope this helps.