Impatiens species- Sikkim
Impatiens for id from Sikkim:: NS Sept 02 : 6 posts by 3 authors. Attachments (5).  
This herb was found near Pelling, please help to identify..
This looks like something close to I. drepanophora or I. longipes (see upcurved spur), but this group of species is particularly difficult and little known.
Are flowers pure yellow? How high was plants? Is this annual or perennial?
One of dividing features between I. drepanophora and I. longipes are glandular tips of beak in mouth of lower sepal and lateral sepals. I don't see this detail good enough on your pictures, however... Whole flower looks like 2-2,5 cm long - is my estimation correct?
I am sorry for not being able to give full information, the flower was completely yellow (however, some specimens from a different location show purple streaks on the upcurved spur), plant was about 1-1.2 ft. high, most probably annual.. your estimation about flowers size is also right..
Some high resolution cropped pics are attached, if they are of any help.. 
I am unable to push this further, unfortunately. 
Some details are missing, some not match descriptions...