Help! Code: "mixture Control, Off Idle"

[Eric S.]

Car: 1999 540/6 Sport

I'm getting a SES light, but after reset it doesn't appear on the first drive; after driving 15 to 20 minutes and stopping, the SES light appears on the way home from such a trip. Twice in a row this has happened and twice I've checked the code with my handy dandy Peake Research R5/FCX-II, and both times I am getting the following codes:
1A - "Mixture Control, off idle, cyl #1-4"
1B - "Mixture Control, off idle, cyl #5-8"
- no other codes.

I get no noticable symptoms that anything is wrong, no stalling, nothing.

So what do you guys think this issue is? I am thinking it's something serving the entire engine since it's hitting both cylinder banks, or else I'd be thinking O2 sensor(s). Does this sound like a MAF Sensor? I'm not getting any stalling tendencies though, at least so far.

As the teacher in Ferris Bueller's Day Off said, "Anyone...? Anyone...?"

I'd really rather avoid Benjamin Dover at the dealer, if possible!

Thanks for sharing your ideas!

[billB]

Eric s: 1A - "Mixture Control, off idle, cyl #1-4"
1B - "Mixture Control, off idle, cyl #5-8"

While O2 sensors are listed under different codes in that little white booklet of peak research as such if your problem was O2 sensor related; in the 540s it should have listed a range of codes between say code 03 to about code 15 or 16. Your codes above are pointing in different direction. Did yoiu fit your car with one of those K&N filters? I have seen many on this forum boasting about them.
billb

[Eric S.]

Originally posted by billB@Oct 30 2004, 11:29 PM
Did yoiu fit your car with one of those K&N filters? I have seen many on this forum boasting about them.
billb

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Nope, totally stock.

I was thinking about it more last night and I think what is happening is that the O2 sensors are actually doing their job in sniffing the exhaust & triggering this code. I am thinking that the two main sensors that would be responsible for fuel/air mix at cruise would have to be the throttle position sensor and the MAF sensor.

I have no idea how to check whether the TPS is calibrated, but now I'll tip my hand and tell you this: I just replaced my MAF before this happened. You may recall my post about about discovering a cracked MAF housing. I was getting no codes. Happyguy had an old MAF that had failed but had a good housing so he overnighted it to me (he also has a 1999 540i/6 Sport). I carefully swapped my "good" sensor piece into his housing (the "tube") and then put it all back together. Drove it 20 minutes, no problem. After 3 hours, returned home and got the code on the way back.

So here we are. It's really looking like the MAF, but it looks like a calibration issue in lieu of a total failure. I was very careful when swapping the sensor pieces, but something must have happened.

Any ideas now? Sorry so wordy, but this is detailed stuff!

[billB]

Eric s
You said it, the reason I was asking you about K&N some of those filters come with oil coating on them somewhat oil hits the MAF and render it caput. What I was getting at is the MAF sensor. Rather expensive piece of electronics $300 plus.

Note:
A. The mass air flow sensor measures the amount of air that is going into the engine. Also an openning in the boot may cause the car to stall and generate this code. (mixed readings/inaccurate data etc)
B. TPS (throttle position switch) also use a potentiometer to measure throttle position and adjust fuel levels accordingly. If the proper amount is not giving; it will trigger the second code.

O2 sensors? I think they are OK

To be sure have it scanned
Good luck
billb

[BeelZibub]

Did you reset the system after replacing the MAF by removing the neg battery lead for 15 minutes? If not now is a good time to do it - even if you did it won't hurt to try again.

[Eric S.]

Originally posted by BeelZibub@Oct 31 2004, 03:03 PM
Did you reset the system after replacing the MAF by removing the neg battery lead for 15 minutes? If not now is a good time to do it - even if you did it won't hurt to try again.

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Thanks for the tip, but tell me - is it as simple as that? Can I truly disconnect my battery for 15 minutes, reconnect it, and all will be OK and operate except for my radio station memory presets? I heard that ONly a dealer could replace an E39 battery (here in the USA) thanks to trade agreements in place with Germany since 1995. Wives tale?

[billB]

Eric s

K mart has batteries for the E39s. Mine is a sears diehard for the last 3 years no problems..self installed.

[Eric S.]

Brief Update -

Figuring it's probably my Frankenstein MAF (see my note above), I saw no reason not to take it apart again to look for anything suspicious (I'm already looking at buying a new one, right?). I found a tiny piece of lint or something inside the pitot, which I carefully removed with a scrunched-up Q-tip. Upon re-assembly, I put an oh-so-thin layer of Permatex Ultra Black (hi-temp RTV) on the top mounting surface of the housing (in case any air was leaking past that internal O-ring), between the sensor elex itself and the plastic housing.

I think this is my best shot. I'll also reset everything by doing the negative battery terminal disconnect for 15 minutes tonight as well. Past that, who knows? Also, I know that it takes awhile after reset for the code to re-appear (about 25 minutes of driving), so if it's going to re-appear, it will likely do so on my way home from work tomorrow night.

I'll keep you posted, (I was hoping you (Bill & Beelz) would respond, thanks!).

PS - I think I can get that Bosch MAF at "Atlantic British" parts for $263 + $10 Shipping, as sold for a Land Rover (same part). The next best I saw was All-OEM at $284 with free shipping. Everyone else is over $300, and my dealer is priced at $451!!

[BeelZibub]

Originally posted by Eric S.@Nov 1 2004, 04:18 AM
Brief Update -

Figuring it's probably my Frankenstein MAF (see my note above), I saw no reason not to take it apart again to look for anything suspicious (I'm already looking at buying a new one, right?).* I found a tiny piece of lint or something inside the pitot, which I carefully removed with a scrunched-up Q-tip.* Upon re-assembly, I put an oh-so-thin layer of Permatex Ultra Black (hi-temp RTV) on the top mounting surface of the housing (in case any air was leaking past that internal O-ring), between the sensor elex itself and the plastic housing.*

I think this is my best shot.* I'll also reset everything by doing the negative battery terminal disconnect for 15 minutes tonight as well.* Past that, who knows?* Also, I know that it takes awhile after reset for the code to re-appear (about 25 minutes of driving), so if it's going to re-appear, it will likely do so on my way home from work tomorrow night.

I'll keep you posted, (I was hoping you (Bill & Beelz) would respond, thanks!).**

PS - I think I can get that Bosch MAF at "Atlantic British" parts for $263 + $10 Shipping, as sold for a Land Rover (same part).* The next best I saw was All-OEM at $284 with free shipping.* Everyone else is over $300, and my dealer* is priced at $451!!

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The thing is you should disconnect the battery lead before you even touch the MAF by the time you're done the comp. will have reset itself and upon start up will recalibrate itself - any changes to the intake/mixture/sensors really requires a reset of the comp. so a recalibration can take into account the changes.

If this doesn't work then probably you will have to go for the new sensor - It seems these rather expensive little sensors are a typical problem on the BMW.

Good luck

[Eric S.]

One more update -

OK, after picking the micro-lint out of the MAF sensor pitot tube, and sealing the elctronic piece back onto the housing as dexcribed above, AND doing the battery-disconnect reset, I drove the 540 for nearly 70 miles today in 4 separate trips, and guess what - NO SES LIGHT!! B)

Based on how reliably the SES came on before (after about 25 minutes of driving), I am fairly certain this problem has been solved!

So, I avoided the MAF-Replacement Mambo (for now). As a side-benefit, the car is burning more rubber than Teresa Heinz Kerry burns bras, thanks to the adaptive memory reset from the battery disconnect.

This will hopefully better enable me to address a couple of other scheduled major replacements due at 100K (I am at 103K): spark plugs, O2 sensors, brake fluid, and coolant, for starters...

[billB]

Way to go wishing you the best