2001 X5 3.0 misfire codes

[DillonInCO]

Hi there! First post here, hopefully I'll be able to stick around with more than just questions about problems...

I'm looking at buying an E53. There's one locally that's perfect for me---I like the color combo, it's a 5-speed (must have for me), and it's got the options I want. It also runs and drives great, for having 148K on it. Seriously, I never expected an SUV to be so fun to drive. The catch? The SES light is on, returning a group of codes, which I assume are all related. Now, being a DIYer, I figure this might be an opportunity to talk the dealer down on price and fix the problem myself. So, I'm hoping to compile a list of what all could possibly be wrong, and from there, figure out whether it's worth the trouble.

Here are the codes:

P0300 - Random / Multiple Cylinder Misfire
P0302 - Cylinder #2 Misfire
P0304 - Cylinder #4 Misfire
P0313 (x2) - Misfire Detected with Low Fuel
P0161 - O2 Sensor Heater Failure

Anyone had these codes? What was the cause? I want to stress that when I looked at it, it fired right up, and it idled and ran smooth as silk. If the light wasn't on, I never would have known it had a problem.

Here's what I've read are the most common potential issues:

- Bad post-cat O2 sensor(s)
- Fault in the O2 sensor heater circuit
- Clogged catalytic converter
- Fuel pump going out
- Clogged / dirty fuel filter
- Dirty fuel injectors

And less likely, since the car exhibits no real signs of trouble:

- Dirty / faulty MAF
- Large vacuum leak
- Faulty DISA system
- Faulty CVV / oil-air separator system

So basically it could be as simple as running some fuel injector cleaner through the system and as complex as a head gasket. I think a problem with one or more O2 sensors is almost guaranteed. But, could an O2 sensor cause ALL of those codes? It's just bizarre that the car seemingly runs fine.