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We report 4 years of observations of 3C273 at 7 mm obtained with theItapetinga Radiotelescope, in Brazil, between 2009 and 2013. We detected aflare in 2010 March, when the flux density increased by 50% and reached 35 Jy.After the flare, the flux density started to decrease and reached values lowerthan 10 Jy. We suggest that the 7 mm flare is the radio counterpart of the$\gamma$-ray flare observed by Fermi/LAT in 2009 September, in which the fluxdensity at high energies reached a factor of fifty of its average value. Adelay of 170 days between the radio and $\gamma$-ray flares was revealed usingthe Discrete Correlation Function (DCF) that can be interpreted in the contextof a shock model, in which each flare corresponds to the formation of a compactsuperluminal component that expands and becomes optically thin at radiofrequencies at latter epochs. The difference in flare intensity betweenfrequencies and at a different times, is explained as a consequence of anincrease in the Doppler factor $\delta$, as predicted by the 16 year precessionmodel proposed by Abraham & Romero, which has a large effect on boosting athigh frequencies while does not affect too much the observed optically thickradio emission. We discuss other observable effects of the variation in$\delta$, as the increase in the formation rate of superluminal components, thevariations in the time delay between flares and the periodic behaviour of theradio light curve that we found compatible with changes in the Doppler factor.

3C273 variability at 7 mm: Evidences of shocks and precession in the jet