Sunny 2000 - engine shuts off when idling

I have a nissan sunny 2000 model. For the past few days I have noticed that the car's engine is giving a few knocks while I am on the highway...as if it wants to shut off. Today I went and changed the spark plugs and the fuel filter.

Now the car will shut off when idling. As long as my foot is pressing the accelerator pedal,, the engine revs, but the moment I remove my foot the engine immediately stops.

What is the problem?

I went to the mechanic today. He just adjusted the fuel flow into the engine at idle and the problem stopped. But I have noticed that now the engine revs lot more at idle than before. Was this the problem or was it just a quick fix? Should I leave at at that or should I go to another mechanic?