Cadillac Repair: 1999 Cad. Sedan De Ville Concourse, sixth attempt, intake manifold

Question
The car has only 30k miles. All of a sudden it's decided not to start with just a crank. It takes about 10 seconds of cranking to start and then it feels like it's flooded. But this only happens about 4 times out of 10 starts. Yesterday it took about 15 seconds and gave off with a very load backfire (in the intake manifold I presume) not at the exhaust. I have taken it to the mechanic that normally works on my cars but he can't make it mal function. Always the case huh. Any suggestions?
Thank you,
Ray Elkins

Answer
The next time it fails to start on the FIRST crank, Try this and let me know what happens:

Turn the ignition switch on for 5 seconds and then turn the ignition switch off. Do NOT try and crank the engine. Do this procedure 5 times in a row and on the sixth attempt try and start the engine and see what it does.