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Ask the Mechanic: Why does my car stall at intersections?

A car that stalls at intersections can be incredibly frustrating. There's a few reasons why it happens. Here are three of the most common. You can try diagnosing them yourself.

Low automatic transmission fluid levels

Many people don't realise that insufficient fluid can be a direct cause of stalling. To find out, park your car on an even surface and test levels with a dip stick, being sure to avoid contamination with dirt or dust. Keep in mind, too, that for optimum performance, it's important to replace transmission fluids regularly. Use the manufacturer's instructions as a guide.

A dirty or worn-out idle control valve

Trouble with an idle control valve can cause, not only stalling, but also kangaroo hopping or rapid ticking over. If you're experiencing any of these symptoms, it's important to check it. On some cars, a faulty valve is indicated by the appearance of Engine Code Error (ECE) P1406.

The valve's job, which is executed by the engine control unit (ECU), is to provide the engine with air, even when the throttle has been closed off. If the valve is really worn, or really filthy, it can stick, causing your engine to 'suffocate' and therefore stall.

The good news is that you can try cleaning the valve yourself. You'll need carburettor cleaner, which should be applied to the valve's ports and seat. It's crucial to clean all components as thoroughly as possible. If they're particularly dirty, feel free to give the valve a soak. A good way of drying it is by blowing it thoroughly with an air compressor (if you have one).

If cleaning doesn't result in improvement, it might well be time for a new valve.

Clogged catalytic converter

Are you noticing, not only stalling, but also a loss of power during acceleration? Your catalytic converted might well be clogged. The easiest way to find out if this is the case is to look underneath the car, either in a dark place or at night, after the engine's been running. If your catalytic converter seems to be glowing, there's a very high chance that it is clogged and most likely needs replacing.

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