First of all, is the direct connection still in place? If yes, get it disconnected immediately. Secondly the problem is on CNG or Petrol? Thirdly, do not replace the throttle body with carburetor.
The problem, I think, is with the MAP sensor (A rectangular (3x2 inch) sensor located on the firewall with green harness [grip]..see snap below). Either the grip is loose/not connected or the vacuum pipe is broken/leak. If none of these two, the MAP sensor is faulty. Please verify and report back.