Rick's Free Auto Repair Advice

What causes car stalling?

Diagnose and fix car stalling issues

Common car stalling issues

Car stalling issues are usually caused by one of the issues listed below, or a combination of those problems occurring at the same time. Diagnosing a car stalling issue is much easier if you can understand that engines need the right amount of air, fuel and spark. If they’re not getting one or more of those, you’ll get car stalling issues. Here are the most common causes:

Car stall caused by lack of air or too much air

Engine is not getting enough air, or is getting UNMETERED air

• Idle air control— on mid 2000 and older

A carboned up idle air bypass valve can cause a high idle

Idle air control valve or idle air bypass valve

vehicles, the throttle body plate is fully closed at idle. The only way air gets into the engine is through an idle air bypass valve (IABP). The IABP valve is an electrically operated device that opens and closes based on commands from the vehicle’s PCM/ECM. Car makers use stepper motors and pulse and width modulation (PWM) techniques for solenoids. In a PWM system, the PCM/ECM varies the on/off times to the solenoid to move a tapered pintle off its seat, allowed more or less air into the intake manifold.

• Unmetered air—The PCM/ECM calculates

fix engine misfire

Tear in air intake hose that allows unmetered air into the engine

how much fuel to deliver to the engine based on the amount of air it lets into the engine. If the engine develops a vacuum leak from a disconnect vacuum hose, leaking intake manifold gasket, or a tear in the air duct between the air filter box and the throttle body, you wind up with car stalling issues as well as hesitation, stumble on acceleration, low power and poor gas mileage, and most likely a check engine light if the problem persists for too long.

How to diagnose an air issue

Check the Idle air bypass valve and throttle body

If your vehicle has an IABP, check it for carbon buildup. Remove the IABP and spray the ports with throttle body cleaner to remove carbon deposits. Wipe off all deposits with a clean rag and dry with compressed air.

Next, open the throttle plate and check for carbon buildup in the throat of the throttle body. Carbon buildup can prevent the throttle plate from closing completely. In an engine equipped with an IABP, a partially open throttle plate will throw off the incoming air/fuel balance, causing car stalling. Carbon buildup in the throttle body usually doesn’t cause a problem on a cold start, but can easily cause stalling once the engine warms up and the PCM/ECM reduces idle speed and air/fuel mixtures to an “engine warm” setting. At that point, the carbon buildup may crack the throttle plate open enough that the IABP can no longer compensate for the extra air. Throttle body cleaning can correct this problem.

WARNING: The Throttle body cleaning procedure is different for electronic throttle bodies than for cable operated throttle bodies. Spraying excess throttle body cleaner into an electronic throttle body can damage the electronics, costing you several hundred dollars for a new throttle body.

For more information on cleaning an electronic throttle body, see this post.

Check for a vacuum or air duct leak

Examine the rubber/plastic air duct that runs from the air filter box to the throttle body. Any crack or hole in that duct will cause unmetered air to enter the engine, throwing off the air/fuel mixture and causing a rough idle, stumble, hesitation, poor gas mileage and even car stalling. If you find a tear in the air duct, replace the entire duct. Do NOT try to glue, seal or repair the duct. The repair will NOT last. Replacement air ducts are available from the dealer and dormanproducts.com.

If the air duct checks out, look for a disconnected vacuum hose. If you find one, reconnect it. Next, check for an intake gasket leak by spraying carb cleaner around the intake manifold gasket. A leak will cause the spray to get sucked in quickly. If you find a leak, get it repaired.

What are the symptoms of an air issue?

• Car starts fine when cold, but car stalls after it warms up at idle. At idle speed, the engine can’t handle that much extra air.

• Car stumbles or hesitates on acceleration

• Car has low power and pickup

• Gas mileage drops

What are fuel and fuel filter related symptoms?

• Extended cranking times on cold starts is usually

Ford fuel pump

Ford fuel pump module

an indication of check valve failure. The fuel pump contains a check valve to maintain fuel pressure in the lines from the pump to the injectors. When the check valve fails, fuel drains back into the tank. On a cold start, the pump must re-fill the fuel lines and build enough pressure to start the engine. That can take 5-8 seconds of cranking; far longer than normal.

• Extended cranking caused by leaking fuel injectors. The fuel pump check valve keeps prevent fuel from draining back into the tank when the engine is off. However, if the fuel injectors have carbon buildup, they can remain open, causing them to dump raw fuel into the cylinders when the engine is off. That results in “no pressure” when starting situation and extended cranking.

• Lack of power at higher speeds can be caused by low fuel pump volume. The fuel pump may keep up with fuel demands at idle or city driving speeds, but simply can’t deliver the right fuel volume and pressure at higher speeds.

• Poor acceleration can also be caused replace fuel filterby a clogged fuel filter; the engine simple can’t get enough fuel to match the requested acceleration.

©, 2018 Rick Muscoplat


Posted on by Rick Muscoplat

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