I had basically the same identical problem and it took almost all last summer to figure it out. The problem was a leak in my intake manifold, when the car warmed up it was ok.Part of the problem was I didn't realize that my heads were milled and my intake also had to me machined to match up.If you pull the intake and see any oil at all on you're gaskets you are sucking oil into the combustion chambers via the intake valves.Good luck it's an easy fix if you know where to look.
PANTERA INTERNATIONAL
A DE TOMASO CAR CLUB
Presents the De Tomaso Forums
The On-Line Meeting Place for De Tomaso Owners and Enthusiasts From Around the World
Clicking on the banner will take you to the sponsor's website.