See full version: How to Diagnose and Repair Carburetor Problems
This is a problem that is usually (but not always) the carburetor's fault. The carburetor may flood if dirt enters the needle valve and prevents it from closing. With no way to shut off the flow of fuel, the bowl overflows and spills fuel into the carburetor throat or out the bowl vents. A flooded engine may not start because the plugs are wet with fuel. here
If the carburetor jets are coated with fuel varnish deposits, or there is dirt inside the fuel bowl, this can restrict the flow of fuel causing a lean condition. Cleaning the carburetor with carburetor cleaner can get rid of the dirt and varnish deposits to restore normal operation.
Problems that are often blamed on a "bad" or "dirty" carburetor include hard starting, hesitation, stalling, rough idle, flooding, idling too fast and poor fuel economy. Sometimes it is the carburetor and sometimes it is something else. Carburetors can be tricky to rebuilt, and expensive to replace, so you want to be sure of your diagnosis before you touch this critical part.
Other causes of hard starting include vacuum leaks, ignition problems (worn or dirty spark plugs, bad plug wires, cap, rotor, etc.), low compression, even a weak starter or battery.
Other causes may include a defective distributor advance mechanism, a weak ignition coil, carbon tracks on the coil tower or distributor cap, bad plug wires, worn or dirty spark plugs that misfire when the engine is under load, or even an exhaust restriction. Even bad gas can cause hesitation problems. So before the carburetor is rebuilt or replaced, these other possibilities need to be investigated an ruled out.
One of the trickiest culprits to diagnose is a clogged EGR valve since the manifestations of a bad EGR valve are almost similar to a problem in the spark plugs, fuel filter, fuel pump, and different engine sensors. However, one of the classic manifestations of a clogged EGR valve that leaves the valve wide open is vehicle stalling. When the valve gets stuck in the open position, there’s a continuous movement of exhaust gases back into the engine via the intake manifold. The increased levels of exhaust gases in the engine interfere with the car’s optimum fuel-air ratio. This reduces power and can lead to stalling.
When a car dies at idle, the last thing that drivers think of is a problem with the spark plugs. Gasoline engines require these small gadgets to deliver a spark to ignite the fuel air mixture in the combustion chamber. If you have a diesel engine, then this is something that you don’t need to worry about. The way diesel engines produce power is different from gasoline engines. Every time the injectors push fuel and air into the chamber, the spark plugs deliver the electrical current. This keeps the engine running. If you have a weak or poor quality spark plug, then it is possible that it will lead to car stalling.
One possible answer to the question, “why is my car stalling?” is a problem in one of the many sensors that connect to the engine. These sensors monitor different parameters to keep the engine running at optimum performance. One of these sensors is the mass air flow sensor. This keeps track of the amount of air that enters the intake system and the combustion chamber. If there is a problem with this sensor, then it can send faulty signals to the car’s computer. The engine will also not produce the optimal power it used to. With sub-optimal power, the car will not be able to continue running when it is at low speeds. The same is true with a bad or dirty oxygen sensor. This sensor tells the computer if there is too much oxygen in the fuel air mixture or too little oxygen. This way, the computer will make the necessary adjustments in fuel delivery. If it gets the wrong information, the engine may not get the right air fuel mixture for proper combustion.
If your car stalls at idle, one of the possible causes is a problem in the idle air control actuator. This component is responsible for managing the RPM of the engine at idle speed. It connects to the car’s electronic control unit, allowing it to make the necessary adjustments for a more efficient, safer, and smoother idle speed. Unfortunately, if the actuator gets damaged, the engine will no longer receive signals that tell it at what speed it should operate when idling. Hence, it stops. The same thing can happen if the system gets clogged. Excessive carbon buildup can also prevent the more accurate measurement of engine speed. This can also lead to a situation where the car stalls when stopped. here
If you have an automatic transmission vehicle, stalling can be a sign of a malfunctioning torque converter or a torque converter solenoid. The torque converter is the equivalent of the clutch in a manual transmission vehicle. As such, its principal function is to transmit power to the rest of the drivetrain. Damage to the torque converter can undermine its power-transmitting capabilities. This is most often felt at low speeds and can lead to vehicle stalling. A problem with the solenoid can also be a reason why a car stalls at idle. Another potential transmission-related cause of car stall is low transmission fluid levels. The good news with such an issue is that it is very easy and inexpensive to fix. Just check the level of transmission fluid in the car and top off to the required level. more
A problem in any component of the car’s fuel delivery system can also result in vehicle stalling. For instance, a failing fuel pump will not be able to provide the engine with fuel from the tank. This can lead to a reduction in fuel pressure, resulting in an inconsistent flow of fuel to the engine. At high speeds, this is not a problem. The problem occurs when the engine is running at low speeds. A pause in the flow of fuel can kill the engine. Defective fuel injectors and low pressure fuel can also cause a vehicle to stall when it is running at low speeds or when it comes to a stop. It is often wise to have these components checked on a regular basis to save yourself from the frustration and embarrassment of having a stalled vehicle. here
This has been going on for a couple months. I am getting no error codes. Short list of things I have tried: [links]
My car drives fine in the city and on the highway. When the engine is cold or cool it will idle normally around 800-1000 rpms. Once the engine is warmed up to near the half mark on the temp gauge in the dash the car will stall or try to stall if idling for one minute to five minutes. The rpm's will drop to 500-800, engine will shake, and either stall out or surge up to 1300 rpm's before going back down to 1000. When the rpm's are low if I press the gas nothing happens or the car stalls out immediately. This only happens once it is warmed up. I have consistently let it idle for fifteen to twenty minutes when cold and no problems. Sometimes I get a very light white-grey smoke from exhaust for a couple of minutes. A quick note it always starts right back up after stalling. more
Replaced Camshaft Position Sensor.
Replaced Throttle Position Sensor.
Replaced Battery.
Replaced IAC Valve.
Replaced Spark Plugs (one had a little oil on it).
Cleaned Throttle Body.
Replaced PCV Valve hose.
Cleaned EGR Valve (had a fair amount of carbon build-up).
Transmission fluid level is good.
Replaced Air Filter.
Oil level is good.
Coolant level is good.
No fluid leaks. [links]
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Tom: I’d start with the points and condenser. They’re cheap and easy. If they don’t fix it, ratchet up to testing the coil. If the coil is fine, put in the Zenith carburetor. [links]
Ray: Over time, what happens is that the float develops little, tiny pinholes in it, and becomes porous. And it gets to the point where, basically, the float barely floats! more
Ray: I’m confident one of those things will fix it, Will. But if not, don’t write to us again. Remember, the reason you never see questions about old farm tractors in our column is because we don’t know anything about them! [links]
Ray: So, while you said you’ve put in new plugs, you really need to put in points and a condenser, too. And you even might want to test the resistance of the coil, to be sure it’s still putting out sufficient voltage. [links]
Tom: You might have a classic case of float sink. Carburetors regulate the gasoline flow with a float — just like the one in your toilet tank. Most of them are made of plastic, but yours may be old enough to be made out of copper. Or maybe granite!