RPM is jumping when car is stopped then feels like it might stall. Then AC blows cold till I stop then starts blowing warm. Once I move again it blows cold. Can these be related? What can it be
My car has 174000 miles.
My car has an automatic transmission.
What you are describing sounds like a dirty or failing idle air control valve. The idle air control valve monitors the air intake as it is mixed with fuel prior to being injected into the engine at low speeds and at idle. This valve is controlled by the vehicle’s computer and will adjust idle speed based upon other measurements such as engine temperature, intake air temperature and electrical system load or voltage. This is also an important function when starting the motor as it allows the motor to run and idle on it’s own once the motor fires. When you accelerate, the engine RPM increases, and as you let off the gas, the RPM slowly returns to the normal idling speed with the help of the idle air control valve making the transition from a higher RPM back down to idle speed while adjusting the air/fuel ratio constantly to allow this to happen smoothly. When the engine RPM drops below the normal range of about 750-800 RPM, this often times will cause the engine to stall indicating a dirty or faulty idle air control valve.
The AC cooling problem when stopped may be related to a bad condenser fan that may not be working properly. As you may know, the job of the AC condenser fan is to cool down the AC condenser as it generates a lot of heat during the course of its primary function, which is to convert the AC gas refrigerant into a liquid form, a process that generates a significant amount of heat. As the AC condenser fan blows cool air across the condenser, this allows the condenser to remain cool, keeping the pressure down in the AC system which helps to generate cooler air. This is much more noticeable when the vehicle comes to a stop or is moving slowly. As the vehicle accelerates, the air moves past the condenser cooling it naturally as the vehicle travels down the road requiring less effort on the part of the condenser fan. I would suggest having a professional from YourMechanic come to your location to take a look at your vehicle.
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