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The 2.8L motor in the Z3 is the same motor found in the E36 so the process is almost identical.
First remove the intae, MAF and inlet hose that leads to the throttle body. Take the fuel rail cover off, unbolt the fuel rail and remove the wiring line to the injectors. Then unbolt the bolts holding the intake manifold to the head. They arent torqued down very hard, but they are a pain to remove. Unbolt the 4 bolts holding the throttle body to the intake manifold.Unbolt the intake manifold to the bracket underneath it. Now you can take the manifold off.
Here are a few links with pictures:
Any other questions, feel free to ask!