  We analyse a set of three RXTE Target of Opportunity observations of the
Galactic microquasar GRS 1915+105, observed in April 2000. We concentrate on
the timing properties of the source, and examine the properties of a low
frequency QPO, with its harmonic, in several energy ranges. The source was
found in two different states of the spectro/temporal classification of Belloni
et al. (2000), and exhibited in the three observations a strong, low frequency
QPO together with a strong harmonic. We discuss the properties of the QPO, of
its harmonic and of their spectral behaviour in the framework of the Accretion
Ejection Instability (AEI) (Tagger & Pellat, 1999; Varni\`ere, Rodriguez &
Tagger, 2001; Rodriguez et al., 2001).
