To check the ignition wires open the hood after dark and look for crossover sparks.
The spark plugs should be changed and gapped to .35 to provide better performance.
If all is good above I would get a volt meter and see if it is the fuel system failing to provide by checking the o2 sensor.
o2 sensor readings.
You can check it on your diagnostic plug though.
Use a VOM on pin 15.
.6 volts is dang rich .3 volts is dang lean.
http://www.kemparts.com/TechTalk/tt07.asp 
http://www.unofficialbmw.com/images/reset1.gif
1. Ground
4. Temperature sensor
7. Reset
8. TDC sensor yellow
9. TDC sensor shield
10.TDC sensor black
11.Start signal
12.Alternator charging excitation voltage
13.Ignition coil
14.Alternator charging supply current
15.Oxygen sensor output to test with.
Later,
Linear Mode
