My 96 chevy blazer only starts when I spray starting fluid in the intake. So far I have changed the starter and battery, fuel filter, and a shop ran a system cleaner through it. It does nothing but cranks until I spray into the intake, and it's only after it's been sitting for a while. I have to use the spray in the morning before I leave for work, but when I go to lunch it starts right up, it's seems to only be when it sits for more than six hours. It's a v6 and 4X4. What could be the problem?