Crankcase Breather?

Hi guys,

Given the bad weather I've been doing very few miles in the Jetta.

I start it up every weekend, let it get up to temperature, and then take it for a quick spin. When it is warming up it runs fine, but when it is at normal running temp it cuts out and is hesitant to start again.

There is plenty of fuel, and the fact that it runs beforehand tells me there's no real leccy problems.

I did notice though, the crankcase breather hose keeps popping off the bottom of the airbox, so I tried the car with and without. Without, it runs much better and at slightly higher revs. When I put it back on, it either runs lumpy or just cuts out.

This can't be normal surely?

Thanks for any help.

sounds like you air filter might be clogged up? or the intake is restricted? This would account for why when the breater pipe is detached, air can easily reach the carb and it runs smoother.
When heating up the car normally needs a richer mixture so the problem isnt so noticable.

Could be wrong though  

Cheers,
Matt