I have SEARCHED for the past week to see if anyone has had the same problem.
I might've skimmed through some stuff but its the same answer anyways.

Car: 1993 325is
The light had illuminated and I had left it on for about a month.
I bought an O2 sensor and replaced it.
Drove it around the block, light went out. :buttrock

CEL light never came on until a month and a half later.

I purchased a BMP fault code tool and the codes came up as "Lambda control #1" & "Oxy Sensor".
So I figured that I reset the codes incase it threw me some faulty codes.
Start the car and the CEL is out. I drive it about a block and its illuminated again. :mad I use the code reader again and the "lambda control #1" code doesnt appear but the "Oxy Sensor" is still there. ?????
There is no rough idle or any other symptons of a bad o2 sensor.
I also notice that at periodic times that the light would go out (for about 5 secs or until I shift into 2nd) and then come back on and stay on.

I have brought it to my mechanic who specializes in BMW and Mercedes and he has told me that it could be my O2 relay.
I just wanna hear everyone elses input before I pay $70+/hr


Thanks.
Excuse me for another CEL thread :(

BUMP.... :help

COULD be the relay! BTW, if your mechanic specializes in Bimmers, why would you not trust him?

not meaning to bud into your thread but if your car is idoling rough that means u need new o2's right? my car is idoling like this.... best in words... soft soft then light purr light purr repeating.... i need new o2's so yea but is this a symptom of needing new ones?

COULD be the relay! BTW, if your mechanic specializes in Bimmers, why would you not trust him?

I trust him but I just want to hear everyone elses input before I get charged 75/hr just to install a relay or whatever the problem is. :D

:help :help :help :help :help

I put in my O2 Sensor relay, reset the CEL.
Drove it around the block CEL pops up again.
I read the code and now its telling me its my "Lambda Control #1".
I reset it again and drive to my house.
I pull into my garage and read the code, No more lambda code. Now I got the Oxy Sensor code again.
Still no signs of bad O2 sensor.

What else could be wrong?

Need to remove variables first.
Did you use factory spec 02 Sensor?
Try erasing the code without using the BMP tool,
( I have had two faulty quick scan tools).
Do a hard clear, disconnect the battery for a few minutes, be prepared with the radio security code.
Start the engine from cold and let it idle in the driveway until fully warmed up,
Any CEL ?
If your CEL comes on in the first few minutes during warmup you may have a failure of the 02 heater circuitry, get out the manual and the digital multimeter.
If you are clear in the driveway without a CEL then go for a test ride.
If you start to get an indication, try to note when it happened, during brisk acceleration or just cruising.
Lambda, if I recall correctly, was a term first used in the early days of electronic engine management. The term basically describes the function of maintaining the "stoichiometric ratio", or the maintenance and control of the fuel/air mixture within the required narrow range.
When your ECU is telling you that "Lambda" is not being maintained, your car is not controlling the fuel/air ration within the expectations of the ECU.
Is it a lagging or defective 02 sensor, a failing or fouled catalytic converter, fuel additives that have degraded the reaction time/ability of the cat or the 02 sensor or a failure of the ECU to accurately control the fuel/air mixture during changing conditions?
Do the "hard" clearing of the ECU, then you know you are starting with a clear memory. Would be nice if you had a replacement ECU for test purposes, possibly a friend has one you could swap out?
I have had ECU`s go intermittent with false codes for almost a year before they finally quit. Not saying that this is the problem but your symptoms will be almost impossible to track down without some expensive test equipment.
(Exhaust gas analysis on a rolling road dynamometer for full engine load test, etc.)
Sounds as if your fuel/air ratio is not being maintained at a certain point in the driving cycle, be tough to pinpoint without throwing parts at the car.
andrew

Need to remove variables first.
Did you use factory spec 02 Sensor?

Well I used a bosch.

Do a hard clear, disconnect the battery for a few minutes, be prepared with the radio security code.
Start the engine from cold and let it idle in the driveway until fully warmed up,


I'll try this out. Im soo frustrated with that stupid light.
I finally got hold of my friend who is an apprentice at BMW and he told me to check my connector (One that's attached to the chassis). I remember that day it was slushy and the under carriage was dirty. You think that could be causing it the CEL?

Thanx!!! I'll keep you updated.