We examine the long term ( \sim 10 years ) \gamma -ray variability of blazars observed by EGRET and Fermi and find that for six sources the average flux varied by more than an order of magnitude .
For two of these sources ( PKS 0208-512 and PKS 0528+134 ) , there were extensive observations ( at various observing periods ) by EGRET .
Hence these dramatic variations are not due to a single short time-scale flare , but reflect long term changes in the average flux .
Over the last twenty years , these two sources were also the target of several X-ray observatories ( e.g .
ROSAT , ASCA , RXTE , BeppoSAX , Chandra , Suzaku , XMM-Newton and Swift ) .
While the ratios of the average \gamma -ray fluxes between EGRET and Fermi observations are 22.9 \pm 1.9 and 12.6 \pm 1.5 , their estimated 2 - 10 keV X-ray flux do not show such dramatic variations .
The X-ray emission from such flat spectrum radio quasars ( FSRQs ) are believed to be due to synchrotron self Compton , while \gamma -rays originate from inverse Comptonization of external soft photons from an accretion disk and/or broad line region .
We argue that in this scenario , the only explanation for the uncorrelated variability is that there was an order of magnitude decrease in the external soft photons , while the jet parameters remained more or less constant .
This result indicates that perhaps the accretion and jet processes are not tightly coupled in these sources .