I am curious to know under what conditions there can be combustion in the intake manifold. My car (1974 145 continuous fuel injection) drove just fine to a store. When I was done shopping I returned to the car and tried to start it. There was a pop and then a bit of white smoke came out from under the hood. I found that a rubber hose was no longer connected to near where the idle speed mixture knob is. Re-connecting the hose resulted in the car starting and running just fine. My theory of a leaking injector and parked in direct sun lacked spark. Wouldn't there need to be a timing and valve problem for the fuel to have ignited in the intake manifold ?