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What is with the cold starts?

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By Paul Kaganzi

Posted  Thursday, August 7   2014 at  16:48
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I have a Subaru Forester chassis number SF5-073124, now it has a rough cold start and stabilises after about 30 seconds and it does not do the same until the next cold start. It behaves well after the start without any issues. What could be the issue, I used to think it was fuel, could it be?
Samuel B Sentongo

From your description of symptoms it seems your Subaru has a hard cold start and erratic idling when you start the engine. You may need to share or discuss this with your mechanic. Fuel supply related causes of a hard start such as fuel quality (dirty or adulterated fuel), a faulty fuel pump (or fuel pump relay), dirty fuel filter, a faulty crank shaft position sensor (helps regulate engine computer to deliver correct fuel amounts) are not specific to cold or warm starts. Fuel supply related problems will cause a hard start in warm or cold engine start conditions.

A hard cold start and poor engine idling thereafter can be caused by faulty engine sensors such as the Engine Coolant Temperature sensor (ECT). Electronic fuel injection engines rely a lot on warm normal engine temperature to run well. During cold engine starts of an electronically fuel injected engine, there is a need for the engine computer (ECM) to deliver more fuel to facilitate a quick engine start up (cold start fuel enrichment cycle).

The ECM responds to low engine temperature readings by adding more fuel (fuel enrichment) and to higher engine temperatures by cutting back on fuel (fuel trim). The engine temperature is monitored by the Engine Coolant Temperature sensor (ECT). A faulty ECT sensor may read a wrong hot temperature value which may make the ECM fail to run the cold start enrichment cycle.
A faulty engine ignition system can also cause a poor cold start.

Damaged or worn out spark plugs and ignition coils or high tension leads (if you have an older pre 2000 Subaru SF5) will prevent quick or total combustion (burning) of fuel. Whereas this also affects overall full time performance, it will cause a hard cold start especially as delivered fuel is not burnt. After you sort out the above issues it does no harm to check and clean your throttle valve and the attached idle air control valve. This will improve the quality of engine idling both during cold start and normal engine running.

I drive a Toyota Granvia made in 1996. When I bought it, the air conditioning was not working. Since then, many mechanics have tried to put it right without success. I was made to replace injectors and other components and it worked only for one day. I seek your wise counsel.

You need to find a qualified car air conditioning (AC) technician to check the important components of the entire air conditioning system. Here are the components that should be checked: 1) AC compressor which compresses the freon refrigerant liquid or gas from a low temperature low pressure condition to a high temperature high pressure condition usable for cooling your car.

The AC compressor may have suffered mechanical damage or electrical failure. The correct refrigerant gas is type R134A which also has a chemical lubricant to protect the compressor pump.
(2) The AC condenser which is a small radiator which condenses the AC gas to liquid form for cooling. It fails when it springs a leak or becomes clogged due to corrosion damage.

(3) Evaporator: evaporates the AC refrigerant from liquid to gaseous form by so doing freezing it and cooling the car interior. Often it fails when it becomes corroded and leaks coolant or becomes blocked. (4) Expansion valve: regulates the liquid refrigerant going into the evaporator. Use of poor quality refrigerant or age will cause corrosion blockage or damage.

(5) Accumulator or drier is a filter and storage tank for the refrigerant gas. It fails when it leaks due to age or damage during engine repair.
(6) The AC system hoses which are a combination of alluminium, steel and rubber pipes which need to be checked for leaks due to cracks or damaged seals. A good AC service technician should be able to carry out a comprehensive leak test using a special dye and ultra violet detecting torch. Often failure of AC systems is due to the undetectable leaks.