1998 s70 help

[fillyfloater]

Hi, been a regular reader to help me with my volvo but this is my 1st posting.
I have a 1998 s70 (non turbo) with about 133000 miles on it, about a month or so ago it was starting rough.
I took it to autozone to see the check engine code which was faulty coolant temp sensor.
Using your site I saw that it looked like an easy fix.
Since the weather up here (Buffalo NY) is cold and snowy I didn't get to the repair until yesterday.
I bought a new coolant temp sensor and thermostat (since they are together) and followed a posting to do the repair.
The only problem was that after I was done and I ran the engine to get it hot to open the thermostat to refill the coolant from the overflow tank, the engine stalled (it ran for about 10-15 mins the 1st time) I restarted it and it stalled again after about 5-10 mins. Ever since then it has actually started maybe four times in the past 24 hours (after trying maybe 50 times)
any suggestions? i might have to have it towed somewhere now!