  A sample of classical IntraDay Variable (IDV) and IDV candidate sources has
been monitored with the Urumqi 25m telescope and the Effelsberg 100m telescope.
Aim of the project is to investigate the origin of IntraDay Variability, a
phenomenon which has been observed in about 30% of flat spectrum radio quasars.
Simultaneous Effelsberg-Urumqi observations demonstrated that the Urumqi
antenna, although relatively small in diameter, is well suitable for IDV
experiments. A few Urumqi datasets, however, turned out to be affected by a
spurious $\sim 24$ hours modulation, an effect which has been removed by means
of a new procedure for data reduction. In about 14 months, 12 epochs of
observation have been collected, for a total observing time of more than 45
days. The epochs are regularly distributed over the whole year, in order to
check for the presence of systematic annual changes in the variability time
scales - a crucial test for verifying the consistency of source-extrinsic
models of the variability. Preliminary time-analysis of the monitored sources
revealed some hint for a slowing down of the characteristic time scales of
S5~0716+714, a result that, if confirmed, would be compatible with a
source-extrinsic origin of the variability, in contrast to previous IDV
studies. No significant modulation of the time scales has been detected for
S4~0954+658.
