My first thought is a leaking fuel injector flooding one of the cylinders. You might see black smoke out the tail pipe when the engine starts. Proof would be found by installing a mechanical fuel pressure gauge and watching to see if pressure drops overnight. Pressure should be maintained for weeks without running the engine.
Another thought is a MAP sensor that is starting to fail. The engine computer uses this sensor to take a barometric pressure reading before cranking the engine, then it measures manifold vacuum after the engine is running. The computer also wants to see a change "from start to run". If the sensor reports a value outside the acceptable range, it could cause the computer to command insufficient fuel for starting. Wide-open-throttle causes an abnormally high voltage from the throttle position sensor which is a default voltage that causes the computer to temporarily disregard the MAP sensor. Usually MAP sensors fail rather quickly but they could slowly fail over a period of days.
Engine block heaters warm up the coolant, not the external sensors. Even if the engine starts easier with a block heater, that still doesn't solve the original problem. You want to fix the problem, not cover it up.
Friday, January 8th, 2010 AT 3:33 AM