ETUDE IDLING PROBLEM

I have a 2000 Mazda Etude 1,6-litre (DOHC) with a high idle problem. When the engine is at operating temperature, it idles at 1 200 to 1 500 r/min for approximately 10 seconds before settling down to a more normal idle speed of around 950 r/min. I have tried a new air-flow sensor, coil packs, plug leads and had the throttle housing serviced, all to no avail. I do not think the engine is fitted with a lambda sensor. CHARLIE MILLS Boksburg The idle condition is always a tricky one, as there is very little air and fuel reaching the combustion chambers during the idle condition and any small defect influences the idle stability and speed. We will assume the car’s engine is serviced with new air and fuel filters.

There are a lot of checks that you can do before changing parts. Follow them in this order:

• Look for air leaks on the intake system, including the small vacuum pipes and even the hose clamps.

• Clean the idle-control and throttle valves (hopefully this was done when the housing was cleaned).

• Check that the throttle cable is not sticking and the throttle valve returns to its “closed” position when you let go of the throttle pedal (you can manually close the valve at the linkage to check).

• Inspect the engine-temperature sensor. If the ECU cannot get a reading, it defaults to an operating-temperature running map, which is not ideal.

• You’ve changed the air-flow sensor already and state there is no lambda sensor in the exhaust. Make sure no catalyst is fitted in the exhaust, as it would have a lambda sensor to read the air-fuel ratio. You can use a gas analyser to check that the air-fuel ratio is correct.

• You can disconnect the battery for a couple of hours and reconnect to see if it resets the ECU to the default idle condition.