My hba1c is 6,6. this value means values of glycemia 120-140( mean). why my basal glycemia is 88(8 hours fasting) and 81(4 hours fasting)? insulinoma?

Not an insulinoma: I'm betting that your blood glucose rises more than is optimal between meals, but stays in the good range when you're not eating. This is commonplace. Your physician can guide you so that you stay healthy. Think about incorporating plenty of physical exercise in your daily routine; this may help as much as or more than diet and meds.