Well it's plausible but the numbers seem suspicious (I think). Your meter's manual refers to measuring capacitance/resistance in "parallel mode" by default, but that this can be changed to "series mode". This suggests that it is trying to compute the equivalent parallel resistance of the network. The real part of the impedance of a parallel RC network is
\$\frac{R}{1+\omega^2R^2C^2}\$
... and this is frequency dependant. The equivalent parallel resistance in this case is constant with frequency (by definition it is R) and this is what I would expect the meter to display. However in a real capacitor, the equivalent shunt resistance is not formed by a real resistor.
It would be interesting to switch to "series mode" if possible and see what the numbers are then.
Since I am exciting with voltage and reading the current I assume I have a ratio of current to voltage which is admittance.
More specifically, you can call this a trans-admittance, since the voltage is applied at one port of the filter and the response current is measured at a different port.
If you just talk about an "admittance" people will at least at first assume you are talking about the voltage/current relationship at a single port.
Do I convert to current correctly? Do I find conductance and susceptance correctly? Did I understand correctly that the values I measure is admittance?
I didn't follow through your calculations entirely, but you did not come up with the correct result for this case. Your result may be correct for the normal admittance to impedance conversion for a one-port network.
For converting transadmittance to transimpedance you have to consider both ports of the network.
The admittance representation is like this:
\$\begin{bmatrix}I_1 \\ I_2\end{bmatrix}=\begin{bmatrix}Y_{11} & Y_{12} \\ Y_{21} & Y_{22}\end{bmatrix}\begin{bmatrix}V_1 \\ V_2\end{bmatrix}\$
To get the Z-parameters you need to invert the Y matrix. Rather than calculate the inverse by hand I looked it up on Wikipedia, where I found the result for the Z21 term is
\$Z_{21} = \frac{-Y_{21}}{Y_{11}Y_{22}-Y_{12}Y_{21}}\$
Separating this out into real and imaginary parts is of course another algebraic effort, which I'd much rather do using software (Mathematica or whatever) than sort through by hand.
Best Answer
Step:
1) Disconnect the power source from the motor. Use the DMM and set it in resistance mode to measure the DC resistance. Your resistance should be in the range of 0.1 ~ 50 ohm or so depending on the motor type.
2) Assuming that your power source is a sine wave at 230V, we know that
Vrms = Irms * |Z|
|Z| = sqrt(R^2 + X^2)
23 = sqrt(R^2 + X^2)
X^2 = 23^2 - R^2
X = sqrt(23^2 - R^2)
Since you know R, you can find X.
This, assuming that the motor is stalled when you have measured the current. If the motor is allowed to rotate, back emf comes in and this solution is no longer valid.