OK, DU car mechanics...

[Columbia]

What is wrong w/ my car?

It is a 1996 Mazda Protege with 150k miles, manual transmission.

Here's the problem:

The engine revs around 1,000 RPM when idling, but after driving for awhile, I'll push the clutch in when stopped and the RPM drops rapidly and the car stalls.

Any ideas about what's going on?

I really can't afford to take it to the shop as I think the car is on its last legs anyway and I've already spent too much money on it recently. So, hopefully it is something that can be easily fixed on my own.

[bigendian]

1. First and cheapest thing to do.

I assume it is FI so get under the hood and check all vacuum hoses for leaks and bad connections.

1K RPM is not too bad. 900K is better.

There is also a temperature sensor controlling the throttle body I think.

[Columbia]

4. Thanks

I checked the hoses and connections earlier today and things seemed ok, but I'll double-check in the morning.

[Carni]

2. Have you tuned the car up in a while?

Was it raining when this happened?

I am not a mechanic, but a common cause of stalling is leaking Ignition wires (and a cap and rotor if that year had them)

That stuff should be replaced every 50 thousand miles.

[Columbia]

3. Tuned up just a couple months ago

No, it wasn't raining when this happened. It actually happens everyday, but only when the engine is warm.

[KG]

5. AKAIK, there's a switch that controls your idle speed

when you have clutch engaged. mayhap it isn't working correctly.

[Ready4Change]

6. Wild guess: Coil Pack?

Certain years of Miata's have a problem called "idle drop" which sounds a little like this. It's a sign that the coil pack is beginning to fail.

Don't know if your Protoge's engine has similar behavior or not.

[The Traveler]

7. Possible causes

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.

[Columbia]

8. Wow, thanks

Yeah, the service engine is on too, forgot to mention that.

Based on your response, I have a sneaking suspicion that it may indeed by a bad O2 sensor. I'll take it to an AutoZone tomorrow to make sure.

Really appreciate the great advice guys! :yourock:

[The Traveler]

9. My pleasure, bud ...

Let me know how it works out.

[DiverDave]

10. PCV valve

I had the same thing happen to my 87 Accord.
Ran fine, but get to a red light, it would die.
I was skeptical that that was it, but I replaced it and it ran fine.
Give it a try, it is a cheap part.