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Model Code: L31
Engine: Mazda B6 (as I understand it, although stamping not yet sighted on the block itself)
Odometer: approx. 105,000 km

Symptoms: As the vehicle comes to a halt at intersections, the engine will sometimes stumble & on the odd occasion cut-out altogether. The vehicle is normally used for transport to & from work. This drop in engine speed tends to happen more often in the morning (around 7.30am). It rarely occurs on the journey home (around 4.00pm), after the vehicle has been sitting in the sun all day. So perhaps the fault is temperature related. The stumble will also happen once in a while when driving at normal speed of say 50 km/h, although safety at intersections is currently the main concern.

The vehicle is regularly serviced by a generic auto service centre who have so far been unable to identify the cause of the problem. Apparently no engine fault codes have been generated by the PCM. I understand all the regular service items have been taken care of, with the possible exception of the fuel filter which will likely be replaced this weekend.

It is appreciated that dozens of potential faults could cause these symptoms and I have already spoken briefly to one of the AA technicians on the phone about this. I recall that the advice given was to start with the basics and eliminate possible causes one by one, which makes good sense.

One engine component that has been tested so far is the Idle Air Control (IAC) valve, part# B6BF-20660. Haynes manual# 36751 gives the acceptable resistance range across the 2 pins of the IAC valve solenoid as 10.7-12.3 Ohm. The actual resistance here is 14.0 Ohm, which I understand may cause the IAC valve to react slowly to the instructions sent from the PCM. The text book also says that the idle speed should increase from about 700 to 1200 RPM when the electrical connector for the IAC valve is unplugged with the engine running. In this case, the engine RPM does not noticeably increase at all. So it does seem there is a problem here. There may be something else.

At this stage, I am simply inviting comment on the situation. The vehicle will probably soon be going to the local Ford service centre for more comprehensive diagnostic testing. I note that a new IAC valve would be a considerable investment, as the last price Ford had in their system for this part was $671 + GST. It may have changed subsequently. If the entire job were to cost around $1,000 that would be approaching perhaps 40-50% of the car's total value - although it is still an excellent, comparatively low-mileage vehicle in other respects. The difficulty is the intermittent nature of the problem - there is a chance that the engine will behave perfectly on the day that the Ford mechanics look at it, time will tell!

I shall post further developements as they come, perhaps someone else with this model of Ford Laser will benefit from the thread.

Thank you.

You should ensure that the IAC valve and where it fits into is clean. It would be best to get the vehicle to a Ford service centre for diagnosis.