  We report on the X-ray time resolved spectral analysis of XMM-Newton
observations of NGC 3783. The main goal is to detect transient features in the
Fe K line complex, in order to study the dynamics of the innermost accretion
flow. We reanalize archival observations of NGC 3783, a bright local AGN, for
which a transient Fe line was reported, complementing this data set with new
available observations. This results in a long set of observations which can
allow us to better assess the significance of transient features and possibly
test their recurrence time. Moreover, since the new data catch the source in an
obscured state, this analysis allows also to test whether the
appearance/disappearance of transient features is linked to the presence of
obscuring gas. We detect discrete features at the >=90% significance level both
in emission and in absorption at different times of the observations, split
into 5ks time-resolved spectra. The overall significance of individual features
is higher in the obscured dataset. The energy distribution of the detections
changes between the two states of the source, and the features appear to
cluster at different energies. Counting the occurrences of emission/absorption
lines at the same energies, we identify several groups of $\geq3\sigma$
detections: emission features in the 4-6 keV band are present in all
observations and are most likely due to effects of the absorber present in the
source; an emission line blend of neutral Fe K$\beta$/ionized Fe Ka is present
in the unobscured dataset; absorption lines produced by gas at different
ouflowing velocities and ionization states show an increase in energy between
the two epochs, shifting from ~6 keV to ~6.7-6.9 keV. The representation of the
features in a time-energy plane via residual maps highlighted a possible
modulation of the Fe Ka line intensity, linked to the clumpiness of the
absorbing medium.
