Cadillac Repair: Cadillac sputters, fuel pressure regulator, repair history

Question
Hi BIll:

I have a pristine 1991 El Dorado, 105k miles. No repair history other then usual brakes, belts,  but the transmission has been rebuilt (5 years ago).After sitting overnight in the garage, it is now sputtering/knocking upon ignition for just a few seconds. Never happens any other time. Local garage could'nt find it needing anything except a fuel filter. They suggested I need to do more highway driving or that it could be bad gas. Has been happening too long now for either of those reasons. Any ideas? Thanks much.
Linda

Answer
Hi Linda, If you had a fuel injector or fuel pressure regulator that was leaking gas into the cylinder after the engine shut off and the upon start-up it would run rougher until the gas got burned out. The best thing to do is leave it at the shop overnight so they can monitor injector leaking and see if the other sensors are in a normal operating range. They could even lift the rail up high enough to see if any drops are forming on the injector end while the rail is still pressureized. This problem would be best to be taken to someone famillar with the Eldo and not just someone that hangs a sign saying we fix that. Sorry I can't be more help. Bill