PD Golf V starts very poorly

I'm having a problem with my Golf V PD 105 hp (manufactured in 2007).

The car, when left standing overnight, usually takes about 30 seconds to start! This problem doesn't always occur, but it happens most of the time!
He's revving it up completely, and then after about 30 seconds, it starts! It's like he's missing his diesel!
Since the tandem pump was leaking, I thought that must be the problem! I've just resealed it, but the problem still persists!

Does anyone have any idea what that might be?
Possibly the pump in the tank? I was told that this has a check valve, and it's possible that the valve is open, which could allow fuel to flow back into the tank.

Quote:

Perhaps the pump in the tank? I was told that this

has a check valve, and it's possible that this valve is open, which could cause the fuel to flow back into the tank ?????

If that were the case, the problem should be less noticeable when the tank is full.

Based on my gut feeling, I would say the PD units are leaking.

Okay, I've never observed that behavior with a full tank. I'll test it, though!
Thank you.

Hello!

Okay, I tried what you suggested about the tank, but it doesn't change anything!

I've now replaced the seals on the tandem pump, and it's leak-free!

It still doesn't start properly if it sits for a day!

I'm about to lose it with this car!

Check the idle speed (using VCDS)!