The most common cause for tihs code is an improperly malfunctioning front O2 sensor. However, there could be a number of other causes. For example, vacuum leaks, dirty air filter, improperly operating ECT, etc.

The first thing I would do is work on the O2 sensor. Often, the sensor is so funked up with crud, that it doesn't operate properly. To clean it, do the following:

- unscrew sensor from exhaust line (if it is the original, don't be surprised if it is basically seized by being cross threaded and/or overtorqued, in this case, penetrant won't help much, but a torch will)

- heat the node of the sensor with a torch until it glows orange, and keep it this hot for 2-3 minutes

- wait till the sensor is cool enough so that when you spray the non-chlorinated brake cleaner on it, that it doesn't sizzle

- spray non-chlorinated brake cleaner on the sensor (at this point, you should see quite a bit of crud being washed away by the brake cleaner, considering you just burned off 95%+ of the contaminants, that's a heck of a lot of crud)

- wait for the brake cleaner to evaporate

- heat the node again with the torch until it glows orange again, for 2-3 minutes

- you may also want to open up one of the slits in the node a little (this often helps with rich and lean problems)

I used to pull front O2 sensor codes every couple months, then weeks, then almost everyday. At that point, I was full and ready to put in a new O2 sensor. But, an engineering friend of mine explained why it was failing, and how I could fix it. So I did, and I have just explained how to do it.

Even if you find that it was an vacuum leak or a clogged air filter or a faulty ECT, you will probably want to clean off the sensor, as running rich will foul the sensor very quickly.