I have a 96 Honda Civic that I absolutely love and have been driving for 15 years now. For the last few months, I've been dealing with an intermittent rough idle. I took it in to try to fix the problem a few times, and the mechanics have done a number of things, including replacing the sparks, spark wires, and distributor, cleaning the fuel injectors, and pulling the timing belt. Nothing fixed the problem.

Recently the problem has gotten much worse, to the point where the problem is no longer intermittent, the roughness is at all speeds and not just when idling, and it is so bad that the car dies after 30-60 seconds of running every time.

Strangely, even with the car dying, the computer has not thrown any error codes.

The mechanics say that there is low pressure (60psi) in all 4 cylinders. Fuel injection is at spec.

Since it's all 4 cylinders, it makes me think the problem is not in the engine (valves, carbon buildup, seals, head gasket, crack in head) because that should affect the cylinders separately.

Could this be the catalytic converter blocking flow? The upstream O2 sensor is rusted into the converter, so we haven't been able to remove it to test. The mechanic can force the sensor out, but that would mean paying for a new converter and sensors, even if that isn't the problem. Should I force the O2 sensor out, probably making me replace the converter, even though the converter is not necessarily the problem?

Any ideas? What should my next step be?

 

Have you adjusted the valves, ever? If a valve is too tight it will idle poorly and have low compression because the valve doesn't close all the way.

Blocked converter makes the car very slow when you try to drive, but usually idle OK. So I don't think it's that.

And bad O2 sensor will almost always throw a code. Unless maybe you have the HX model? The DX / LX combined manifold and cat is prone to cracking which causes some driveability problems and usually a primary sensor code.

 

I had the valves adjusted, but it was a while ago -- maybe 60k miles. But if it was a bad valve adjustment, wouldn't it be just one or two cylinders, not all at once with equal low compression?

I have the DX model, so the converter/manifold are combined. The O2 sensor isn't throwing a code, but the reason we're trying to remove the upstream sensor is to circumvent the converter and test to see if that's the problem. If the converter is the problem, removing the upstream O2 sensor should cause the engine to run perfectly. Of course, the sensor is seized up and removing it will probably strip the threads in the housing, meaning I've got to get a new manifold/converter as well as a new sensor.

The real problem is that we don't know what next step to take. It looks like it's either the converter or the engine. But it doesn't look like the converter (as you say, rough idle usually means it's not the converter) and it doesn't look like the engine (no error codes, affects all cylinders equally). Either way, the next step will be expensive: to test the converter it means probably breaking it, and to test the engine further it means taking the head off.

 

60 psi compression means that there's something wrong with the engine. Take the valve cover off and check that each rocker arm goes slack when the valve is supposed to be closed.

 

We checked the valves and they seem to be good. Unfortunately, though, we just did a wet compression test, and compression went up to 110. That means that the seals on the pistons are going bad, and that means rebuilding or replacing the engine. Ugh. Plus, it seems like my problem might be more than just low compression, since it still ran rough even with the higher compression.

I've had this car for 15 years, but it looks like it needs to retire permanently.