Rough Idle/Check Engine Light - solved

[chazsandiego]

Lately I've been having issues with rough idling and a check engine light. The rough idle also changes the exhaust odor and sapps my mpg. Cleaning and swapping used Idle Air Control Valves will temporarily resolve the issue but it's back within a couple weeks. Stomp test gave me code 1222 Lamda (o2) sensor.

Is there a way to test wether the o2 sensor or the IACV is throwing the CEL? Could a bad IACV cause the O2 sensor to have issues or vice versa?

Any input on this situation would be greatly appreciated!

[shogun]

O2 sensor can be tested with a voltmeter, see shop manual https://www.bmwtechinfo.com/repair/main/481en/index.htm
https://www.bmwtechinfo.com/repair/m...es/4810056.jpg
Pull the fuel pressure regulator vacuum hose and check if there are gasoline drops inside, then the diaphragm inside is borken

[chazsandiego]

Thanks shogun, I will give that fuel pressure regulator a look, it's been replaced recently but it's not any trouble to check.

I'm sure I can hunt down the plug for for that O2 sensor by tracing the cable back from the cat region. But if anyone knows exactly where it is off hand I'd greatly appreciate the protip

[shogun]

You can test the O2 sensor also another, easier way, from the top of the motronic.
Here I made a write up http://www.bimmerboard.com/forums/posts/622383/
unfortunately the imageshack pics do not work anymore nowadays. You have to remove the top cover of the connector on the Motronic that you have access to the pins from top
Here a pic I made from a Motronik M1.7 with Bosch end # 352 for the M70, so you get an idea http://www.bilder-upload.eu/show.php...1524115135.jpg


hope one of the 2 links works, same pic

Download the pic to your PC!. That free upload server kicks the pic out and deletes it after 200 days.

[chazsandiego]

Wanted to update and put this thread to bed!

O2 sensor was long done.
Had to drop part of the exhaust to make enough space to loosen the sensor.
I'd read in another write up about a $16 O2 sensor removal tool... BUY IT! Unless you have a lift and very tiny hands life is going to be rough.
By the time I realized how invaluable that tool was I'd already cut the sensor wire in an attempt to slip a wrench over it.
I was lucky enough to have a box end wrench that was able to get the job done (with plenty of struggling still).
Drove one way with the new sensor in, no issues but on my way back home all previous symptoms had returned.
As a last ditch effort I threw my original idle air control valve back in and thankfully all problems have been solved! Turns out I had a bad o2 sensor and IACV everything is working amazing now.

Even though I really didn't want to drop the exhaust, when I did a huge rock fell out from somewhere underneath the vehicle. Turns out the rock had been causing an intermittent and mysterious rattle while reversing or accelerating from a standstill. And I'd been thinking it was a noisy driveshaft u-joint....

Much appreciated for all this assistance as always!