98 XLT - Check Engine Diagnostic Codes

[cdash]

My check engine light has been on for a while and I finally stopped by a local Auto Zone for the free diagnostic. I had three codes returned, but have no idea what they mean; PO171 (bank1), PO174 (bank2), and PO300 (which I was told means more than 3 cylinders are mis-firing). I cannot seem to locate any reference for these codes. The vehicle seems to be running fine. Any idea where I can find a reference so I can fix whatever the problem may be. I need to get an inspection and it won't pass with the light on. If all esle fails, is there an easy way to reset the check engine light?

[cdash]

I searched a bit more and found that the codes mean "System Too Lean Bank 1" (PO171), "System Too Lean Bank 2" (PO174), "Multiple/Random Misfire" (PO300). Seems like the misfires are a symptom of the engine is running too lean. Would a bottle of Fuel System Cleaner help clear this problem? Or should I switch to a higher octane fuel as a rule? I have always used the "cheap gas" (87 octane) from Mobil. I have noticed a considerable degredation in fuel economy over the past several months as well. I read that disconnecting the battery will clear the performance memory of the computer- thus improving gas mileage and overall performance. Thoughts?

[Opera House]

You sure it wasn't P0303 miss cyl #3. With it being an outside cyl, I would suspect lower intake manifold gasket leak. Have you been loosing small amounts of coolant? These lower gasket problems are just so common. I have it in my 97 and sometimes only get 4K before a plug fouls. I tightened up the bolts but will probably do the gasket this summer. Is the wire boot for the MAF in place? Cleaning MAF might help. Look for vacuum leaks like splits in air tube. Look at the plugs. A lot of people have problems with BOSCH. Battery will clear codes. If your state now tests with OBDII connector, you will fail if you don't have at least 25 clean cycles at time of test.

[cdash]

It was definitely PO300. The attendant at the Auto Zone didn't seem too bright. He interpreted the code incorrectly. I did have a coolant leak recently, but had it fixed a few weeks ago. The hose clamp to the radiator had completely rusted through and when the system pressure built up, the leak would appear. Difficult to diagnose since it would not leak upon a refill. I did clean the MAF yesterday. I will look for vacuum leaks and look at the plugs. I had the plugs and plug wires changed 37K miles ago at 100K. Thanks for your suggestions.

[JODTRIK]

I have an Expedition that had the same codes. They suggested I change the O2 sensors, did that the light still came on. I finally found I guy that missed his calling as a technician and works at Auto Zone he told me the too lean reading means I had a vaccum leak. It didn't sound like I had any leaks but low and behold after removing all of the lines I could reach and having them inspected I found one with a small rubber boot with a fine crack in the elbow. Changed it for $17.00 no more light and no more problems. When it goes too long it will cause rough idiling. Hope this helps.