Starts good cold. Starts bad when cool

[Wduval]

Hello. So I’ve got a 2002 alh jetta. Recently I’ve ran into a starting issue. I’m pretty sure it’s fuel related.
the Car starts flick of the key after sitting outside all night in -20. I get to work and shut it off. Then at lunch I go and start it and I have to crank on it for 10–15 seconds in order to get it to start.
I think it’s getting air in it somehow. I could be wrong. When I shut it off with the hood open I can see a bubble of air coming from the injection pump and floats back to the fuel filter. So I was thinking it must have some kind of leak.
cant find any fuel leaks. Or anywhere that air might be getting in. Injection pump was leaking after I did the hammer mod.I resealed the pump and it didn’t fix it.
i am just confused on why it starts beautifully after sitting all night in cold weather. But then starts bad after sitting for a few hours
Any help is appreciated

 

[TPW]

I had a problem like that until I changed the glow plug timing.

 

[P2B]

How big is the air bubble? Up to about 1/2" is normal. Bigger then you might have a cracked thermostatic tee or leaking o-rings where the tee plugs into the fuel filter.

Does it make a difference if you double cycle the glow plugs? If so perhaps your temperature sensor is misreporting at cool temperatures.

Where is the timing set? Slightly advanced is best for colder climates.

 

[TornadoRed]

You might confirm that you do not have a sticky anti-shudder valve (ASV).

 

[Wduval]

It’s only a couple small air bubbles that go down the line when I shut it off. I figured it wouldn’t be enough air to cause starting issues.
And I’ve got a darkside intake manifold so I don’t have any ASV or egr valve