Questions and Answers

Mazda 626 Cold Idle Problem Q. Dear Vincent, I came across your email id on the net. I need some advise on what could be wrong with my car. I'm giving below some details about the car, the problem and my observations. 1988 Mazda 626 GLX 2.0 liter 1998 CC, 12 valve Compression ratio 8.6 : 1 Manual transmission 246,000 kilometers Carburetor

The Problem:
I'm living in Vaasa (Finland). Temperature now is in the range of -5° to -10°C. I'm only getting about 5 km per litre of petrol (95E). I took the car to a service station. The timing was checked. The emissions are okay when the engine is warmed up. Therefore the fuel consumption is also probably okay on a warm engine.

My observations:
I preheat the engine with an electric heater (two hour timer) before I leave for work. On starting the engine, the smoke from the engine is dark. One can see black soot particles on the snow. I can also smell petrol (probably unburnt due to excess injection). The rpm is about 1,600 - 1,700 rpm when idling.

When the engine is sufficiently warm (engine coolant temp about 80°C), the rpm drops to about 850 rpm on idling. The engine also seems to run quite smoothly then. I've observed the smoke in the warm condition: it is not black. and there is no smell of unburnt fuel.

I've observed that it takes about 6 - 7 km of driving to get the engine sufficiently warmed up. My office is about 5.5 km from my residence. I think that by the time the engine gets warmed up, I'm reaching my office and shutting off the engine. So the choke is always activated, leading to high fuel consumption.

In my opinion, there are two things I need to do:

1) There is some problem with the carburetor of fuel injection system. I'm saying this because of the black smoke during starting and running with cold (relatively cold) engine.

2) The coolant temperature does not increase to 80°C until I drive about 7 km. Therefore the choke is unable to open the air passage to normal level.

For the first point, I do not know what to check. For the second point, I think that by changing the thermostat in the coolant circuit with a thermostat of higher temperature setting (say 80°C), the engine water will by-pass the radiator until the set-point. It may therefore heat up faster to 80°C, i.e., within a distance of 2 km. Thus the choke will de-activate faster and allow normal amount of air to get to the cylinders.

Please advise me on what could be the problem. Also advise me on the actions I must take to correct the problem. Looking forward to your early response.

Thanks and regards,
Suraj

A. I'm pretty sure the problem is with the choke mechanism. When the engine is cold, take off the air cleaner top and look down the carburetor throat. You'll see a butterfly at the very top. This is the choke butterfly. Now step on the gas pedal once with the engine off. The choke butterfly should close. If it doesn't, then you have choke problems.

If it does, the next thing to look for is how it opens. Start the car and watch the butterfly. The choke pull-off will open the butterfly slightly when the engine starts running. Assuming, of course, it's working. As the engine warms up, the choke butterfly should open slowly until it is fully open. This will take about ten minutes, max.

If it doesn't open as I described, then it's possible the choke heater is bad or not receiving power. There is a wire going to the choke heater, make sure it has power. If it does then the choke heater needs to be replaced. If not, check the fuses and ignition circuit.