good to hear you only need the 5 dollar seal, and at your mileage I would definitely say the plugs could use replacing (NGK set is 40 bucks)

My car was noticeably smoother at 68k miles when I replaced the plugs. And obviously if the air filter is dirty it will help too. Did you find excessive oil on any of them?


You may want to try the old mechanics trick and spray WD-40 over vacuum hoses in the engine while the car is running, if you hear the idle dip or rise, you found your vacuum leak :)

the engine's running characterics change with the SES light because the computer shuts down the info flow from some of the sensors and runs the engine on predetermined, fixed values that do not reflect the actual state of the situation...

there are many codes generated during the engine (and the whole car) operation, most of those codes do not trigger the SES light, they are just stored in the memory... at some point, they may reach a threshold that trips the light but if the condition does not manifest itself again, the light resets, while the codes are still stored in the system. if the code (problem) severe enough, the first code can turn the SES light on, and some SES codes do not reset once the issue is gone, you need to clear them from the memory.

most OBD readers will read basic, industry standard codes, and those codes are present in the OBD II socket... however, since the BMW went away from a dedicated round shaped data port and integrated the info flow into the OBD port, that port also has a wealth of BMW specific information that can be pulled by a BMW specific software and being manufacturer specific protocol and info flow, they packed a lot of info into that data port...

you should try to get yourself diagnostic software and a cable (many folks here used the romanian dude on ebay for the package deal) and see if you can monitor your car, both live and just reading the modules...
or, find a friend who has the package already on their laptop... but remember, this is just another tool in your toolbox, it does not replace all the other recommendations you heard here before...

Vacuum leaks
 

Side Note. Spraying wd-40 to look for vacuum leaks is crude and will only work if the leaks are generous. Seafoam, brakecleaner, carb clean, anything works, just not as elegant as a smoke test.

The best way of checking for vacuum leaks is to perform a smoke test. If you are a gearhead and have other projects, it is worth $50 or $60 to purchase a smoke making device. I use one designed for the DJ (think fog filled room and disco). It is cheap and easy to use. Just hook up to any vacuum line and turn the machine on.

You will be able to see if there are vacuum leaks any where, not just where you squirt the wd-40 or whatever you use.

It runs rough with the SES light on because for some DTCs the computer will shut down the injector(s) in order to prevent damage to the CAT. With the injector(s) shut down now you have one less cylinder firing.

You may have a slight miss (which you may not be able to detect) which allows the cylinder to fire but the computer will know that the cylinder is missing.

I have not seen a post where the MAF sensor has been cleaned or tested. Since MAF contributes to fuel mixture it can be the cause of lean codes and or pre cat O2 sensor faults.

I suggest cleaning the MAF thoroughly with MAF cleaner, easy to do and doesn't cost much. If you do so, be sure to spray all wires, liberally several times-- after you give the wires a good spraying you can tell where they are back to like new and where you haven't sprayed enough.

True, I haven't tried cleaning the MAF, I didn't have the proper cleaner when I was checking things last night. Can anyone post procedure for testing the MAF? I have a multimeter and have done it on other cars, but for the X5 I can't seem to find what needs to be probed and what the readings should be.

One test is to remove the connector from the harness. If MAF is working properly the idle should increase.

The following should help: How To Test A Bosch MAF Sensor - YouTube

If you are not familiar with how to clean the MAF this will help: How To Clean a Mass Air Flow Sensor (MAF) - YouTube Even if do know how to clean it the on screen dialogue is fun to read.

I don't really get what the guy is doing with the nails in the video of testing the MAF sensor. What are they connected to? Isn't that dangerous anyway? Also, does anyone have a link to procedures for testing coil packs?

Small update...I can now feel it misfiring even when the light isn't on. Installed a new air filter, cleaned the MAF, and made sure all the hose clamps on the intake tract are tight. It ran a bit smoother, but not normal. Changed the plugs, and that made no difference. But after looking at them in better light, I can see that 3 of them look worse than the other 3. It's a little hard to tell in this picture...but these are the plugs pulled out in order from the back of the engine to the front.

https://lh6.googleusercontent.com/-P...124_160853.jpg

The 2nd, 5th and 6th plugs are darker / look more fouled. That seems pretty random.

Now, I had my generic scanner hooked up to it, and after a while of idling at cold start it's throwing P0174, system too lean (bank 2). No other codes yet and the light isn't on. But I'm afraid to drive it like this, as I imagine it could cause some damage?

So...next steps? Thinking I will replace the fuel filter first, as that probably needs to be done anyway. Then I suppose I have to pull the intake and check the CCV system. What about the valve cover gasket, could that cause this?