sixto - good question - I don't know if I ever replaced it. I can't remember what part of the exhaust it's on, but it may have been replaced when an exhaust part was changed (I'll have to look at old receipts). I've had the catylitic converter replaced and also had a timevalve stainless system installed. Can the sensor be checked on the car (how)?

porkface - I'll be checking / replacing the electrical components when it gets a little warmer. I would think that if any of those were really bad (enough to drop the mpg significantly) I would have a rougher running engine. I'll also check for vacuum leaks. After that, if performance hasn't improved, I'll ask my shop about checking fuel pressures etc. I change oil every 5k with dino and it doesn't use much between changes (maybe a quart or two).

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07 E350 4Matic wagon, 06 S430 4Matic, 99 SLK 230
retired W210 (x3), W124, W126