'94 Eurovan surging

I just bought a '94 Eurovan with the 5 speed manual. It has 280,000 kms on it. Runs well and I really like it so far. However it has a surging problem in 3rd-4th gear when driving around town at steady throttle. Of course the problem is intermitent also. Any hints or ideas??

Thanks
Richard

I know this is years later but, we had this problem on our 93 we changed the fuel filter, spark plugs and wires, and clean injectors and no more problems..