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Q: The car occasionally idles high until it stalls

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My car has occasional issues while high idling. Half the time I drive it, it would start having issues with increasing RPMs very high until it shuts off. The issue occurs usually during idling or when I stop at the traffic light for instance. The engine starts revving around 750 RPM and keep increasing it and finally stalls, or it would start idling as it should. When the issue happens, the restarting helps. I had the thermostat replaced. I checked fuel injectors. The dealer hooked it up to a scanner and said no error codes showed. What should I do? Thanks.

A: It sounds like this is an intermittent issu...

It sounds like this is an intermittent issue. These are generally the hardest to diagnose because they are just infrequent enough to not trip the ECU into triggering a code, but they still have a fault somewhere. The most common causes of a high idle include: a fault with the MAF sensor, a vacuum leak, or an idle air control fault. To confirm the faulty component, a technician will have to perform a full diagnosis and may need to use the scan tool to monitor various sensor data to locate the problem. A qualified technician like one from YourMechanic will be able to diagnose your high idle issue, and any other relevant problems, to determine what repairs are appropriate.

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