Idling High

1993 MIata, base model (w/o air-con, w/o ps) The idling is erratic, i.e. jumping between 700 to 900 rpm. What will be the problem? The shop recommended adjusting the timing. Is this right? BTW, I think this problem is causing the car to idle rich. Thanks.
Reply to
Eng Soon
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How old are the plugs and wires?

Reply to
Lanny Chambers

Plugs were replaced at 86K miles on 18 Mar. I am not sure abou the wires.

Reply to
Eng Soon

A bad or dying O2 sensor could cause these symptoms as well--once the engine is warmed up a low (or no) signal from the O2 sensor tells the ECU that the fuel mixture is lean, it compensates by making it richer. Too rich makes a wandering idle.

-cliff-

Reply to
Cliff Knight

After some trouble-shootings, the shop pin-pointed to the cat-converter. Thanks.

Reply to
Eng Soon

I believe your shop got it wrong. A bad cat won't cause high idling or rich idling, however as others have mentioned a bad oxygen sensor can cause both, and that will cause a bad cat.

John ('94 Miata) jsgmcclary at cox dot net

Reply to
John

you mean a bad o2 sensor can cause the cat converter to go bad! this sounds really bad. how can I chk the serviceability of the sensor?

Reply to
Eng Soon

The O2 sensor is used to control the amount of fuel injected into the vehicle under idle and cruise conditions. If it's reporting a lean condition to the ECU, more fuel will be injected and the car will run rich. Running rich means more unburned fuel will be 'burned' in the cat, and this may lead to over-heating of the cat, damaging it.

It's possible your cat is already damaged as a result of a malfunctioning O2 sensor, if so replacing it won't fix the root problem and the new cat would eventually be killed, too.

I usually trust the engine check code myself and/or swapping in a new O2 sensor and see if that fixes the problem.

Dana

Reply to
Dana Myers

I usually trust the engine check code myself and/or swapping in a new O2 sensor and see if that fixes the problem.

Dana

If you have the shop manual, a meter and another person to sit in the Miata to do the reving according to directions, you can test the O2 Sensor. If you need to get one to test, I suggest your local auto parts store. MUCH cheaper than getting one through Mazda. I've had to replace my O2Sensor. Had to buy at our local Kragens. Save about $100. ~Cissy Organize Your Sock Drawer :-D Cissy Mazda Miata

Reply to
Expmiata

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