BMW 1999 Z3 Roadster 2.8, misfiring on cylinder 4,5,6, and also random misfire. Have changed 3 out of 4 lambda sensors, changed all the spark plugs, even tried clearing the faults from the memory and swapping ignition coils 1,2,3, for 4,5,6. The MIL light does not come on but the codes came back as misfire on 4,5, and 6. It is running ok untill the engine gets warm and you try to boot it then you get the most awful misfire and a complete lack of power. There is also a strong smell of petrol sometimes. Could you help please its driving me crazy!!!!
Thanks for your info. its shed a bit of light on the matter. 2 of the lambda sensors pre-cat are OE but the one post cat is a generic one, this is due to the fact that the manager would not listen to reason, maybe this is the problem? It does still have the bremi coils l know of this recall and would like to try the coil replacement but without knowing for sure its an expensive chance to take. Anyway it has gone to the BMW dealers workshop now hopefully we will find out what it is.
Was not there a software upgrade for this particular model also besides the coil problem?
Thanks for your response it has been very helpful, cheers.
I will put what was wrong on here as soon as l find out to help others who may be experiencing this problem.

Code readers r OK for easy problems. But when the going gets rough by way of diagnosis, a scanner that shows live datastream is preferable. In ur case, adaptations (multiplicative & additive/aka
long term & short term fuel trim) should be read. Related to this would be the MAF/airflow readings. Same thing with 02 sensor voltages (whether it is a lean misfire or otherwise).
Sans a good scanner or code reader, the most that u can do is
a) check for vacuum or air leaks (pay special attention to the crankcase vent valve/aka cyclone separator)
b) check if u r still using the recalled Bremi ignition coils (it should be Bosch by now)
c) check if the new 02 sensors r 0EM & not some cheap generic
d) check if the 02 sensor wires or coil cables have been interchanged
e) monitor fuel pressure at the fuel rail from cold to hot engine or until the misfires occur (perhaps u have a bad fuel pressure regulator or fuel pump that starves the pistons causing lean misfires)
f) check for injector pintle actuation during same periods (the injectors may be getting stuck when hot).
Other than the above, ur guess is as good as mine since u have very little info to provide.