When my car is idling the rpms and battery gauge drop off and it acts like it wants to die.

When I stop at a light the car acts like it wants to die. When I push on the gas the car seems to have a hard time shifting and it seems like I have to push the peddle down farther to get it to shift. Any advice would be great.
My car has an automatic transmission.
Experienced mechanics share their insights in answering this question :
Hello Nick,
What are you are describing sounds like potentially a dirty or failing idle air control valve which reads the air intake into the engine. The computer uses this data to make adjustments to the air/fuel ratio to keep the motor running smoothly. When this is not working properly, this may cause the engine to lack acceleration and stall in many cases at low speed or in idle situations as you have described. As the engine RPM’s drop, this may also explain the drop in voltage you see in your charging gauge. I would recommend having a professional from YourMechanic come to your location to diagnose and inspect your vehicle.

How to Identify and Fix Common car Problems ?

Our sources include academic articles, blog posts, and personal essays from experienced mechanics :

At idle, vehicle electrical loads may exceed the low speed current (amperage) output of the generator and when this happens the shortfall comes from the battery. This will result in a drop in the electrical system voltage as the battery delivers the additional electrical current to meet the demand.
If the RPMs drop off right as the engine is stalling then the most common cause of this is a bad crankshaft position sensor. This sensor tells the engine computer what the engine RPM speed is and what the position of the cylinders are. If it fails, the computer does not know the position of the engine so it will stall.
When the battery`s state of charge is low, the voltage is raised slightly to quickly put the charge back in. When the state of charge is high, the voltage is lowered slightly to prevent overcharging. If the vehicle has a voltmeter gauge, you may see the voltage move up or down. This is normal.
The idle speed should feel consistent without skipping or slipping. In most of today`s cars, an idle speed of 600 to 1000 RPMs is average. If your car is idling rough, though, it won`t feel smooth. The RPMs will jump up and down, for example, or they`ll fall below 600 RPM (or whatever is typical for your vehicle).
The alternator provides enough power to charge the battery by itself. Still, if you`re idling and have other electronic components powered on – such as your radio or lights – you could gradually drain your car`s battery and potentially leave yourself stranded.
When batteries chemically age. All rechargeable batteries are consumable components that become less effective as they chemically age. As lithium-ion batteries chemically age, the amount of charge they can hold diminishes, resulting in shorter amounts of time before a device needs to be recharged.
Among the potential underlying causes are vacuum leaks, EGR system malfunctions, malfunctioning oxygen sensors, dirty fuel injectors, fuel pump malfunction, faulty spark plugs, a faulty mass airflow sensor, or a faulty throttle position sensor.
Replace the sensor with a compatible one and correctly install the crankshaft position sensor to ensure that the engine runs optimally and safely. A qualified technician can prevent further issues with RPM fluctuations while driving by installing the sensor correctly.
Probably, the most common symptom associated with a bad regulator is flickering, dimming, or pulsing lights. To be more specific, you may notice that the vehicle`s: Headlights fluctuate between bright and dim, without you doing anything. High beam isn`t working as expected.
A car battery, on its own, will have a near constant voltage close to 12V. But sit a car battery in a vehicle, connected to all the normal loads such as lights, wipers, ignition systems etc, and also to an alternator that is charging it… and the battery voltage will vary all the time.
The battery voltage does not drop whilst idling. To charge a 12v (actually about 12.6v) car battery, the alternator needs to produce a voltage of around 14 volts. To do that, it needs to spin quite fast.
A good alternator should maintain battery voltage between 13.9 and 14.8 volts (14.2 is optimum). Even worst-case, with all accessories turned on, there should be at least 13 volts at the battery.

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

When my car is idling the rpms and battery gauge drop off and it acts like it wants to die.
ANSWER : Hello Nick,
What are you are describing sounds like potentially a dirty or failing idle air control valve which reads the air intake into the engine. The computer uses this data to make adjustments to the air/fuel ratio to keep the motor running smoothly. When this is not working properly, this may cause the engine to lack acceleration and stall in many cases at low speed or in idle situations as you have described. As the engine RPM’s drop, this may also explain the drop in voltage you see in your charging gauge. I would recommend having a professional from YourMechanic come to your location to diagnose and inspect your vehicle.

Car died while driving so I replaced the alternator and battery and car won’t attempt to turn over. What else could it be?
ANSWER : The initial failure was likely caused by a sudden fuel system (e.g., failed fuel pump) or electrical (including ignition) faiure. Prior to performing diagnostics be sure you have a fully charged battery that passes a load test. Then, confirm that the engine immobilizer system (security system) is not activated thus preventing the car from starting. If the starter motor is not functioning, check for power to the starter motor when the key is held in the "start" position. If there a large voltage drop at the starter motor or no power at all, you may have a faulty ignition switch but you do have to check out the entire starter circuit, which includes grounds, wiring (some of which is very heavy cabling), fuses, relays, the ignition switch and terminations. On the other hand, if the starter motor is getting power but the starter doesn’t work, then the starter is condemned and replaced. If you desire that a certified mechanic resolve this, please simply request a no start diagnostic and the responding certified mechanic will get the problem diagnosed and repaired for you. Please let us know if you have further concerns or questions as we are always here to help you.

My car will not start Intermittently. I purchased a new battery 2 weeks ago and yesterday the car wouldn’t start. Got a jump and
ANSWER : The issue you are having is probably due to an intermittent fault in the starter motor itself or a deficiency in the starter electrical circuit, for example a large voltage drop due to a poor ground or a high resistance connection. These issues can be readily diagnosed and resolved on a mobile basis if you request a hard starting diagnostic. If you request that diagnostic, the responding certified mechanic will get this resolved for you promptly. Based on Toyota’s Factory Service Manual, the battery should not be disconnected if the vehicle engine is running. The battery acts as a large resistive voltage sink and consequently taking the battery out of the circuit, while the alternator is still running, can create a voltage spike on the car’s electrical system which is not good for voltage sensitive components such as the engine computer. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

When changing the car battery, do you "register" the battery to the car computer?
ANSWER : Hi there. Changing the battery has nothing to do with programming a battery. If the car was flat dead with a battery that lost all of the power because the dome light was on, then when jumped the vehicle will run fine. What may need programmed when the battery is replaced is the key fob. The key fob will lose programming to the computer as the vehicle computer is reset. However, if a 9 volt battery saver was put into a cigarette lighter and the car battery was removed, then the computer will not lose its memory and be just fine. If you need further assistance with your battery, then seek out a professional, such as one from Your Mechanic, to help you.

My car trembles or idles hard when I’m at a temporary stop. It feels like the car wants to move before I’m ready.
ANSWER : This problem may be related to a dirty or faulty idle air control valve. This valve is a unit that reads the air intake as it is mixed with fuel, prior to being injected into the motor. The computer then uses this information to make fueling adjustments.

When the idle air control valve is not working properly, this may cause the motor to be over-fueled or under-fueled, depending on the conditions. This will cause a rough idle as you have described.

It is recommended that you get a certified technician, such as one from YourMechanic, to come to your location and replace the idle air control valve for you.

Water was spilled in the trunk which soaked the car battery. Car won’t start now. Does water destroy a car battery?
ANSWER : Hi, thanks for writing in about the concern with the BMW 320i. If the battery was submerged in water then it’s completely possible for the battery to short out and die. Your friend will need to have the battery replaced. Also be sure to get all of the water out of the trunk. Have a certified technician, like one from YourMechanic, help you guys out if you need assistance with replacing the battery. Good luck.

My battery light is on.
ANSWER : The problem is not the battery, but the charging system is not keeping the battery recharged. The alternator is the most common cause of this, though failing battery cables can also be a cause. I would recommend having the battery cables and alternator tested and checked by a mechanic, like one from YourMechanic, who will come to you and diagnose the problem for you. Do not try and drive it or it will leave you stranded from the battery going dead again. The cables to the battery from the alternator may be bad or the alternator is not charging. Only the testing and diagnosis will reveal the problem.

Car battery dying quickly especially after longer driving
ANSWER : It sounds like the alternator is not charging the battery, when are you driving long distances. Running all the accessories and then shutting it off can cause the battery to be too weak to restart the car. If the alternator is intermittently not charging, then you may have other wiring issues or just an intermittent problem within the alternator. Have the charging system checked by a mechanic after driving it and not shutting it off, to see if the battery is being charged. You may also have a body control module issue with extended storage mode. The dealer can check this mode with the special scanner and checking the extended storage fuse is not installed.