Hello! It's been about two years since I've been on UnitedBimmer, as we parted with our '96 328i a while back ('twas a sad day). But now I'm back with an OLDER Bavarian auto - a stock '95 525i (e34 M50 motor).
I've only had the car for about a week, and I've been busy with summer classes, my baby, and acquiring new Bilstein struts for the car (the front right is actually BROKEN). So, yeah - I've been prioritizing. And though the CEL is on, the car has run well enough to get around. I'm now just getting around to addressing the CEL.
Using the "tube" (Peake code reader), I originally pulled two fault codes: OXYGEN SENSOR and LAMBDA CONTROL. I'm assuming the LAMBDA CONTROL was tagged because of the O2 sensor (the CEL has been on for a while, according to the previous owner).
This may also be relevant, as I know the O2 sensor (multiple???) was replaced one within the last year... The previous owner made MANY short trips of 2 minutes or less, as she lived down the street from the school where she worked. Condensation build-up around O2 sensor & premature aging? They replaced the O2 sensor and a few months later CEL was back on, indicating a fault of the very same sensor(s) that had just been replaced...
ANYHOW, back to the present tense. I pulled the two aforementioned fault codes, then reset the CEL and waited for the light to reappear.
Sure enough, after about 4 minutes of smooth driving today, the CEL is back on. I popped the "tube" on again after running a few errands (about 15 minutes of city driving) and only the OXYGEN SENSOR code was present. I should mention that in park my idle hunts/bounces slightly back and forth between 600-700 RPMs.
Anyhoo, does any of this ring a bell to current/previous e34 M50 drivers? Is the hunting idle typical of O2 sensor failure? AND how many oxygen sensors are in this vehicle (just one, or one upstream and downstream)??? I've ordered the Bentley repair manual, but have yet to receive it, and haven't put the thing up in the air yet.
IN ADDITION to the oxygen sensor fault code, the thermostat is stuck open (during hot summer days in Illinois it takes a while to reach normal operating temperature, and on the highway at night it hovers just above the blue/cold side). Is it possible THAT could throw off the ECU and cause the mixture to be too rich, triggering the O2 code? Probably not... either way, that issue will be fixed by this Wednesday.
ONE other thought - could a faulty MAF be causing the slightly jumpy idle/slight acceleration hesitation, and somehow show up as "oxygen sensor," since that, too, affects the correct air/fuel mixture? (based on anybody's experience, is that typical? Or does O2 sensor ALWAYS mean O2?)
I'm trying to get her back to optimal running condition. We paid $1600, and considering she's pretty clean with 115,000 miles, I think we made out pretty well.
THANK YOU to anybody who reads through all this and has any input. I REALLY appreciate it. I'll be looking forward to your knowledge/advice... Happy driving, and Auf Wiedersehen!