Hey guys,

I have a 1999 Honda Civic LX with 249,xxx miles, everything stock except an AEM short ram that I put on about 5 years ago. About once a month or so, the CEL will come on. While it's on, the car idles very low (probably in the neighborhood of 300 RPM). The next day or even a few hours later, the light will go out and the idle returns to normal. I pulled the code and my code reader said "System too lean", but I don't have the exact code at the moment.

I've noticed no other abnormalities while the CEL is on, just the extremely low idle. And keep in mind this is an extremely intermittent problem. Any ideas? A friend told me it could be a vacuum leak or a bad O2 sensor.

Thanks in advance!
Colin

 

Check if your exhaust manifold is leaking. The LX combined manifold / converter is prone to crack in the center, which will cause bad readings from the O2 sensor.

 

Thanks for the quick reply! And excuse my ignorance, but what would be the best way to check that?

Thanks again.

 

Look for a crack and if that doesn't help, look under the hood and listen to the manifold area while idling for air leaks.

If there is a crack you will probably notice. Make sure to look in nooks and crannies that are hard to see because of the heat shield.

 

I took this picture. I looked for obvious cracks on the manifold and didn't see any. As seen in that picture, there is an area of corrosion on the manifold/converter. However, I started the car and put my hand infront of that corroded area, and I didn't feel any gases escaping so I don't think that's the cause. I'm at work so I don't have a chance to remove the bumper to check more thoroughly, but I checked everything I could under the hood.