Does the alternator affect the idle?

Modern vehicles require a steady electrical current of specific voltage in order to run properly. Drops in electrical output from a failing alternator can cause these systems to malfunction, leading to a poorly running engine. Symptoms will be rough idle, misfires, poor acceleration, hesitation and stalling.

Will disconnecting battery reset idle?

Many newer cars with powertrain control modules (PCMs) have to relearn engine idle after a battery is disconnected. The removal of electrical power from the engine erases idle memory from the PCM, the computer where it is stored. The relearning process depends on the PCM.

Can I check my alternator by disconnecting the battery?

If you’re tempted to test an alternator by disconnecting the negative battery cable, don’t do it. A good alternator may indeed keep the engine running without the negative cable, but this was never a good test. The second you disconnect the battery, the voltage regulator pegs the alternator to put out maximum power.

How does a bad alternator cause high idle?

If your powertrain control computer is misreading idle speeds, this can cause a high idling malfunction. When your car’s throttle is malfunctioning, this can cause your car to stall or idle high. Often this is a result of dirt buildup in the air intake. And a bad alternator can also cause fast idling in your engine.

Which cable do you disconnect to check alternator?

If you’re tempted to test an alternator by disconnecting the negative battery cable, don’t do it. A good alternator may indeed keep the engine running without the negative cable, but this was never a good test. In the pre-computer days, you could pull it off without damaging anything.

How long should I leave battery disconnected to reset ECU?

Disconnecting the battery for a short time may not do the trick because the car’s computer, or ECU, still has some current in it. Waiting for over 15 minutes after disconnecting the engine will help ensure the equipment is reset.

What happens to idle memory when battery is disconnected?

Many newer cars with powertrain control modules (PCMs) have to relearn engine idle after a battery is disconnected. The removal of electrical power from the engine erases idle memory from the PCM, the computer where it is stored. The relearning process depends on the PCM.

Why won’t my car idle high enough?

My car has an automatic transmission. You will need to re-learn the idle for the vehicle to get it to idle high enough. You should first clean the throttle plates and throttle body and idle control valve. When you disconnected the battery, the idle control was reset to factory and will idle differently unless you relearn the idle again.

What happens to an engine when the battery is replaced?

Engine idle is only part of the natural memory, or accumulated data, lost when the battery is replaced. Adjustments to the fuel mixture, transmission shifting and various habits of the driver may all have to be relearned. It may be necessary to use a scan tool to reset PCMs on newer cars and to reset the anti-theft system, according to AA1Car.com.

What does engine idle mean?

Engine idle refers to the lowest rpm or speed at which the engine turns over when the driver is not depressing the gas pedal, according to 2CarPros.com. At idle speed, the engine generates its lowest emissions, thus conserving fuel.