Reply #7: Possible causes [View All]

[The Traveler]

I haven't worked on a Mazda, but there are several likely suspects. A few of them have already been mentioned. First ... do you have a "Sevice Engine Light"? If so, take the car to AutoZone for a free diagnosis. (Other parts stores do this, also, if ya don't have a Zone handy.) Your car is OBDII compliant and the on board computer can usually tell you exactly what the problem is ... setting the "Service Engine" light is its way of telling you it wants to talk.

An 02 sensor can do this. As the engine gets hot, the on board computer will transition from "open loop" to "closed loop" operation ...expecting the O2 sensor readings to be accurate after they've gotten hot. 02 sensor levels are used to control your fuel/air mix ratio when your system goes to closed loop operation. O2 sensors can fail hard (liteally "flatlining") or become inaccurate as they age. In the latter case, fuel/air mix ratio will be miscontrolled, and that can cause a stall at low RPM. In this case, tho, you would expect other symptoms .... rough or hesitant acceleration, for example. O2 sensors are roughly $60 at your auto parts store, but are usually quite easy to install yourself.

If the ignition wires are good, another possible culprit is the electronic ignition module itself. Usually about the same price. Usually an easy installation for a shade tree mechanic. (Again, I haven't worked on a Mazda.) If you were driving a small block Chevy, this would be my first suspect.

A bad vaccuum hose can certainly cause this. An old mechanic's trick for finding small vac hose leaks is to, with your car running, spray Gumout carb cleaner on the hoses. If your RPM suddenly changes momentarily, and you can reproduce the change by spraying the hose down again, you found the leaky hose. Replace it. When in doubt, replace 'em all. Hose is cheap.

You probably have a MAP sensor (Manifold Air Pressure sensor) ... if ya don't you have a MAF (Manifold Air Flow sensor). A possible but less likely prospect.

Feel free to contact me via AIM (screen name a3kelvin) if you want. I'm not an expert but I have turned a wrench from time to time.