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Originally Posted by trekkor
Best investment if you do your own diagnostics is an OBDII reader.
Spend the $200 for a good one.
The one I bought has live data monitoring.
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Absolutley. It's a must-have tool. You can buy a reader-only for under $100, but a better one with some data-capture, graphing, live monitoring would be better. I bought my ~$300 Acctron used on eBay for $75 a couple years ago.
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As far as 'Bank One' is concerned, there should be an O2 sensor before and after the cat.
After the exhaust is hot, you can compare the data to bank two and pinpoint the faulty sensor.
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The readings for bank one (pre cat) and bank two (post cat) SHOULD be different, as the cat should be burning things clean. The two sensors perform different functions, but the computer uses the data in concert to make adjustments.
Since you're getting a bank one code, it is telling you a little more about what the engine is actually doing rather than how clean things are post-cat. If you're getting a lean code, it has to be either too little fuel or too much air. The MAF reads how much air is coming in so if it "thinks" it's getting x volume but is actually getting 1.1x volume, the system will be lean. Or if the fuel injectors aren't giving enough fuel, then it will be lean. An air leak downstream of the MAF will add air to the system, hence 1.1x versus x. If the EGR diaphragm is bad it could add some air downstream of the MAF, but it would/should throw its own code.
As far as the timing thing, you said you were asymptomatic before the timing belt, and actually had your first driveability issues after the change. That's why it was significant to me.
Simply unplugging the ECM for 30 minutes ALSO resets all of the data maps the engine uses. It defaults rather than using what it has "learned". So it may run differently for a while. That's why resetting a CEL with a scan tool is preferred.