Q: iwhen we start my car it ideals at 2000 rpms but when you put it in drive it drops to 1000 rpm

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Ok my mom is using my car in norther Indiana well my alternator went out we got a new alternator replace the belt but now my car idles at 2000 RPMs when put into drive it drops down to a thousand RPMs is this normal it didn't do it until the alternator went out

My car has 100000 miles.
My car has an automatic transmission.

Normal idle speed for your vehicle, once the engine is warm, should be around 750 RPM (roughly). Two thousand RPM is significantly out of range high, even for a cold engine. The occurrence of this high idle speed might be a coincidence and thus not related to the alternator repair. Among the potential causes of high idle is a faulty or blown fuse in other electronically controlled systems which can cause the IAC (idle air control) motor to malfunction, leading to a higher than normal engine idle speed. Other possible causes of a high idle include vacuum leaks, a malfunctioning throttle (throttle plate could be sticking; throttle position sensor could be faulty) and, rarely, a PCM/ECM malfunction. With regard to vacuum leaks, on a fuel injected engine a vacuum leak will cause a high engine idle as the engine’s oxygen sensor detect the extra oxygen entering the engine through the vacuum leak. The newly lean (too much air relative to fuel) status will result in the engine’s computer pumping in additional fuel, resulting in an abnormally high idle. If you desire that this high idle problem be diagnosed by a certified Mechanic, dispatched by YourMechanic right to your location, please request an engine idle speed diagnostic - high idle and the responding certified mechanic will get this taken care of for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

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