HELP! Loss of Power in my BMW Z3!



I have a 1999 BMW Z3 with the 2.3 five speed and 6 cylinder engine. about 2 months ago the engine seemed to be running rough and lacked the normal power and fuel economy i’ve been used to getting.

I replaced the air filter and all the spark plugs, and the problem seemed resolved. now we’re back to the same sort of trouble and i don’t know what to do. Loss of Power and somewhat of a sputter. perhaps a fuel injector problem?

Any ideas?