How do you expect it to cold start well without a functioning air bypass then? Surely you've answered your own question as to why it's bad

Engines are very inefficient when cold with the enrichened afr etc, and are easy to "stall" which is why even from the days of a manual choke a cold starting car was given an increased idle speed to aid stability and prevent it cutting out until it was warm enough to be leaned off and operate normally.

You've turned half the cold start mapping off by cutting the increased idle speed. Why do you think the valve is there?

Best thing you can do is put a STD valve back in, and mod it so it will still function well enough to give you a nice increased idle speed,
Or use 2 valves one STD for cold start, and a second for ALS