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Rough Idling & Hesitation


MAC

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Since the water pump failed and coolant/water leaked onto the wires under the water pump and on the O2 sensor on the exhaust manifold, my Eldorado’s been idling very rough and hesitates when accelerating. When I shut down and restart it will idle much better, at least for a while, but then it will again idle and run rough as I drive.

When I arrived at work I took the negative battery cable off in order to see if a relearn would cure the problem. It’s seems to be better but I will be in a better position to analyze the results as I drive home.

I’m curious as to whether hot coolant dripping onto an O2 sensor can damage the sensor? On the other hand, perhaps coolant fouled-up the harness connection. I’ll take the connection apart and clean it.

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Coolant dripping on things can cause temporary shorts or open circuits, but even anti-freeze evaporates in a couple of days. Are there any OBD-I codes?

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Coolant dripping on things can cause temporary shorts or open circuits, but even anti-freeze evaporates in a couple of days. Are there any OBD-I codes?

I saw one code, P046 (Right to Left Bank Fueling Difference), but it was in history. That code hasn't appeared again. I'm going to get a bucket of water and a little bit of soap and try to clean the entire area of any residual coolant. But I have a feeling that either the O2 sensor failed due to the constant barrage of super heated coolant streaming on it at various times or the harness connection may be contaminated? I’m looking at my GM Service Manual and it says:

The PCM controls the rear bank fueling based on the rear oxygen sensor and the front bank fueling based on the front oxygen sensor. Code P046 sets when the front bank fueling differs greatly (richer or leaner) from the rear bank fueling for 10 minutes.

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It sounds more like you may have a vacuum leak (such as an intake gasket). That would explain the fuel trim differences AND the rough idle. I don't think coolant would foul an O2 sensor, EXTERNALLY. If you were burning coolant through the cylinders, maybe. I've had various coolant leaks over the years (leaking water pump seal, fixed; leaking water pump housing seal, fixed; leaking heater hose next to water pump, fixed). All have probably spewed small amounts of coolant on the front O2 sensor, but none of the leaks have caused a problem with it.

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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