It means your fuel rail pressure is bleeding off overnight. Here is what is going on, the fuel rail pressure bleeds off overnight, when you you go to start it in the morning, it is fuel starved. Waiting 15 seconds gives the fuel pump time to get the fuel rail pressure back up. Causes could be a numb...

To be clear, Not quite, two steps are required: 1. Techron® Complete Fuel System Cleaner - "I always treat my cars to this in the fuel tank every oil change! Doing it for years and I've never had a fuel injector problem in any of my vehicles for the past 30 years. My Mercedes mechanic told me ...

If you fill the tank with gas first, where you going to find the space for the Sea Foam? ........
Put the Sea Foam in first, that way your have the space for the Sea Foam and the two will mix as the tank fills.

No problems with my 1988 760 Turbo wagon as long as I only run top tier gasoline.

I only run top tier gasoline. Many years ago, I had a 1981 VW Rabbit Pickup with Bosch CIS fuel injection, which constally flows fuel thru injectors. Before government mandated a basic detergent package in all gasoline fuels, if I filled up with cheap gas, within short period of time, those injecto...

Your fuel pressure has a slow leak.
1. It could be a fuel line or fuel rail with a slow leak.
2. A leaky fuel pressure regulator bleeding fuel back to the tank.
3. Leaking fuel injectors.

Trace dye would find external leaks but not internal leaks.

Tell the mechanic the fuel pressure bleeds off over night and you got to let the pressure build back up before you can get it started. He should be able to take it from there.

The FPRs are obsolete parts.

First , make sure you need one by monitoring the absolute fuel pressure at idle and at load. Your mechanic should have done this then told you the results. I’m not sure you need to chase that part, failures are rare, if it isn’t full of fuel on the vacuum side