2000 Suzuki Grand Vitara, Coughing and surging

hi, i have recently had my acr to a local mechenic. When i drove it, it coughed and spluttered like it was starved of fuel, i was with out it for 2 weeks, he told me the problem was dirty petrol....so he gave me injecta clean, and told me not to run it under quater of a tank, to avoid sucking up crap, when he dropped it off it was pretty much empty, it went fine for a day and a half, then it started worst then ever!! can someone please help me out??
Cheers Danni Also, he told me he cleaned the tank, blew the lines out and changed filters!! im sick of spending money and getting nowhere...