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25 May 2023 Idle control valve: function, symptoms, and replacement cost
What does the idle control valve do?
In case you aren’t familiar with the term, idling is when the engine is left running but the car stays still. The idle air control (IAC) valve plays a key role in ensuring that the engine idles smoothly and at a consistent RPM. It is located on the car throttle body, which regulates the amount of air flowing into the engine for combustion and, consequently, the speed of the motor. The more you press on the accelerator pedal, the more air the throttle releases into the intake manifold, increasing the engine power. Releasing the pedal will reduce the airflow and RPM. When idling, the IAC valve essentially takes over, supplying enough air to keep the motor running stably and prevent stalling.
Causes of idle control valve problems
- Build up of dirt or grime
One of the most common causes of idling problems is a clogged IAC valve. Over time, carbon deposits and contaminants can build up around the component, obstructing or blocking it completely. This often occurs as a result of using poor-quality fuel or poor maintenance. It may be possible to fix the fault by cleaning the component using a suitable intake system or throttle body cleaner.
- Electrical problems
There is always a possibility that the issue has been caused by a poor electrical connection, particularly in older vehicles. For example, loose or corroded connectors and faults such as short circuits can stop the idle speed control valve from operating properly.
- Air leaks
If there is a fault when idling, it could also be the result of a leak. A vacuum leak can cause excess air to be sucked into the system, bypassing the valve and affecting the air-fuel mixture. This causes the RPM to increase and decrease erratically. The valve itself could be leaking or the culprit may be a worn or broken seal or damaged hose, for example. Rough idling can also occur due to faulty spark plugs, filters and car fuel injectors. It is therefore necessary to check the other parts of a car fuel system.
Article number: 95SKV951
£ 24,51
price incl. 20% VAT, excl. delivery costs
-60%
Article number: 6NW 358 189-011
compared to
RRP
£ 36,04
£ 14,16
price incl. 20% VAT, excl. delivery costs
BOSCH Adjusting Potentiometer, idle mixture
Article number: F 01C 600 328
£ 385,27
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BOSCH Adjusting Potentiometer, idle mixture
Article number: F 01C 600 073
£ 10,87
price incl. 20% VAT, excl. delivery costs
-61%
Article number: 6NW 358 189-001
compared to
RRP
£ 36,04
£ 13,93
price incl. 20% VAT, excl. delivery costs
Symptoms of a faulty idle air control valve
- Rough idling & fluctuating RPM
Since the IAC component is supposed to regulate the engine idle speed, fluctuating idle speeds are a clear sign that something isn’t right. You may notice that the engine power suddenly surges and drops while idling. It’s also possible that the vehicle will start to shake or vibrate excessively due to a lack of air in the combustion system. As mentioned earlier, there are many possible explanations for this, which is why a thorough inspection and diagnosis is required.
- Engine stalling
If there isn’t enough air flowing through the valve, the engine won’t have the power to run and may stall suddenly during idling. Moreover, it can stall when an additional load is put on the power unit, e.g. from the AC system.
- Check engine light comes on
The ECU will warn the driver if it detects an error by illuminating the check engine light on the dashboard. You can either take the car to a professional mechanic or try to determine the cause of the error yourself using a diagnostic scanner.
How much does it cost to replace an idle control valve
In the UK, the cost of an idle air control valve replacement may vary depending on the make and model of the vehicle, the specifications, and labour rates. If you look for the part online, you’ll find prices ranging from £12 to just under £500. DIY repairs are cheaper as long as the job is done properly. Checking and cleaning the component every so often can also save you money in the long run.
If you’re shopping for replacement parts online and want to narrow down the search results, you can do so by entering certain details such as the specific car make and model along with the part name into the search engine or on the website, e.g. “Ford Fiesta MK6 idle control valve”. You could also enter the vehicle’s unique identification number to find compatible parts.
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