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Q: My car has a low idle and will stop at lights or stop signs

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The problem with the car developed gradually where it eventually idled so low that it would stall at startup or at a light, I have replaced the serpentine belt, mass air sensor, PCV valve, coolant temperature sensor, oxygen sensor, air filter and spark plugs, and next I'll change the throttle position sensor, not worried about changing all of these sensors and things, it was probably about time to. 1 mechanics said that it was the Transmission lock up, because the car stalls when put in Drive, but does not stall when put in reverse, but that does not make sense to me because if I give the car a little gas, it will not stall in drive and will operate normally until I slow down to stop at a light and the idle becomes so low that it stalls again. My question is, can a Transmission lock up malfunction in that way, only at idle and only in forward? Also couldn't the throttle position sensor be a better answer?

My car has 159000 miles.
My car has an automatic transmission.

A: Hello. The symptoms you describe can be ca...

Hello. The symptoms you describe can be caused by a few different things. A few other possible causes are issues with the idle air control valve, with the transmission, or with the throttle position sensor. The idle air control valve is the component that maintains and adjusts the engine idle speed, and can cause all sorts of issues, including stalling, if it has a problem or fails. Similar symptoms can also be caused by issues with the vehicle’s transmission.

If one of the sensors or components, such as a speed sensor, shift solenoid, or the shift interlock solenoid have an issue they can also produce the symptoms you are experiencing. Another possibility is the throttle position sensor. Though less likely, it does play a role in the vehicles shifting and idle behavior. Stalling can also be caused by a wide variety of other issues, such as problems with the fuel, ignition, or engine management systems.

I would recommend having a professional technician, such as one from YourMechanic, come to your location to determine if the cause of the stalling.

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