Cadillac Repair: starting problems, fuel pressure regulator, mass air flow sensor

Question
Hi Ben
My name is Terry I own a 1998 Cadillac Deville 4.6 northstar
and i have had starting problems with it I  have already changed the coolant temp sensor, air filter, mass air flow sensor, fuel pressure regulator, spark plugs, spark plug wires, fuel filter, and all four of the coil packs it doesn't want to start after taking a trip like 30 minutes or so but it will start after 2 turns or one long crank the owner before me used regular unleaded and i seen that the car calls for premium so i put premium in the car and it triggered the check engine light because it just didn't want to start i took it to advanced auto parts and it pulled up all kind of sensors this problem comes and goes OH YEAH WHEN I CHANGED THE FUEL PRESSURE REGULATOR THE PROBLEM SEEM TO GET A LOT BETTER AFTER CHANGING ALL OF THIS STUFF BUT IT STILL ACTS UP A LITTLE i read in your list that the fuel pressure regulator are known for leaking and over fueling but if that was so my car would be hard to start up in the mourning right but it cranks right up in the mourning if i let it set for hours or over night it starts right up but its when the car is warmed up and then i let it set for about a hour or less is when i have trouble any help would be greatly appreciated

Answer
Not neccessarily, when a car is sitting for over 4 hours the motor will be pretty much completely cool, the left over gas in the cylinder will be sitting at the bottom, this is where carbon gets built up. Try flushing your motor with gunk motor flush, and then sea foam it. Change the oil after.