The oxygen sensor is one of the most important elements of the modern fuel injection systems. A finely tuned fuel injection system with an oxygen sensor can maintain an air/fuel ratio within a close tolerance of .02 percent. Keeping the engine at the stoichiometric level (14.6:1 air/fuel ratio) helps the engine generate the most power with the least amount of emissions.
There are a few signs that your oxygen sensor may be failing. In general, it is difficult to diagnose problems with the sensor, unless all of the other components in the fuel injection system have been checked and determined to be operating correctly. Some of the symptoms of a failed oxygen sensor system are:
Irregular idle during warm-up
Irregular idle with warm engine
Engine will not accelerate and backfires
Poor engine performance
Fuel consumption is high
Driving performance is weak
CO concentration at idle is too high or too low
Check Engine light is illuminated
In general, if the oxygen sensor is not working, the car will be running very poorly, and will also be outputting a lot of harmful emissions. On most BMWs, the engine's computer will give you a warning signal that lights up the Check Engine Lamp if the signal received by the computer is out of it's normal range...
In general, it is recommend that we should be replaced this every 30,000 miles...
Many E36 owners upgrade their chassis with the factory crossbrace that mounts underneath the engine. This crossbrace was installed as stock equipment on all convertibles and the 1995 LTW, a lightweight version of the M3. The convertibles received this bar to stiffen up the chassis since their chassis are naturally less stiff than coupes or sedans because they have no roof.
Installing the crossbrace on a standard E36 coupe or sedan serves a dual purpose: The crossbrace stiffens up the chassis and also protects the engine sump from road hazards.
reference from: http://www.pelicanparts.com/bmw/techarticles/101-Projects-66-X-Brace/101-Projects-66-X-Brace.htm
M52/M52TU Straight 6 DOHC 24V with Single VANOS/Straight 6 DOHC 24V with Double VANOS. 1996-1999.
Iron Block in US, Alloy Block in Europe . 118kg 260lbs (alloy) 140kg 308lbs Used in E39 520i/523i/528i, E36 323i/328i, E38 728i, Variation of this was used in late US E36 M3. 2.0 (150bhp), 2.5 (170bhp), 2.8 (193bhp), 3.2 (240bhp) Sometimes referred to as S52US.
Engine shares more common parts with M52 than Euro S52, but is a motorsport engine.
reference from: http://www.bimmerforums.com/engine_faq/