The impedance of a throat mic system (condenser) is about 1 billion ohms, if that helps. hehe
To actually be helpful though, I don't think any of the throat mic systems are dynamic or carbon, they should be a condenser system (super high impedance). That 150ohm spec out is specific to old dynamic (military conversion) boom acoustic headset microphone systems. As far as I know any throat mic system (non military) should work with your iCom. If you have a very old military tactical throat system, the system is low impedance and will not work without some type of amplified impedance converter.
Also, be sure that you are depressing the PTT switch when transmitting. The vibratory triggering for those throat mics are notorious for not squelching properly. It may not be working because the pickup is not triggering. I'll also tell you that NIH and NCBI did significant testing on boom(acoustic) mics and throat(condensed) mics. They used the MRT (Modified Rhyme Test) and found that intelligibility using throat mics is significantly poorer than with the use of boom microphones in noisy and in quiet environments. Throat microphones are not recommended for use in any situation where fast accurate speech intelligibility is essential.
Another issue people have is mistaking the little twin plug connector. Make sure the connector is for an iCom radio, not a Motorola, Rap4, Vertex, or a Kenwood plug.
Having said all that, I know that iCom makes there own throat mic system as well. If memory serves it's an HS-97. Single side pickup and one ear plug though.
This is not a sales pitch at all, it's just fact. The only way that I know to remove the wind & ambient noise in open cockpit / ultralights and use your existing headset/helmet,or our headsets is the
PA9-EHN mic. I'm serious. It's the best thing ever.