You cannot generalize Indian IQ as it varies tremendously amongst various sub population. Rushton and others disregard the high IQ results by Indian in the US (Hindus have the highest SAT scores as a subgroup) by claiming that this is because of selective immigration, and then take other results of lower IQ by indian immigrants as gospel, which is also a selective group.
There are two types of immigrant from India. Initially Highly skilled Indians emmigrated to the US. This was the initial wave. Then their spouses and other relatives also emmigrated. This subset was not as intellectually gifted. Then there are the economic immigrants. These are typically people who are not doing too well in India. Part of the reason is that they could not compete in India. This is the labor class, and probably has low IQ. This is what is found in Fiji, Vancouver, Gulf, and Carribean. You cannot make generalization by just looking at one group.
Britain probably has the most representative sample of immigrants. It has the doctors and engineers, along with the lower economic class people. IQ tests have shown that Indians in Britain have an IQ of 97, despite having a verbal disadvantage of not speaking English in majority of homes. Another study has indicated that as a group, Hindus do better than white english school children.
Most of the population in India is rural, and their brain does not get the stimulation that is needed to do well on these IQ tests. However if you question them in their area of expertise, they have good grasp of nuances in agriculture engineering that is needed to be a succesful farmer, rural businessmen, street vendor etc. There is also a subsection of population that is regressive and dumb, and they tend to belong to the tribal and/or lower caste population.
I would say that there is a population of 300 million in India with IQ comparable with that of white america. This essentially represents the so called middle class in India . Then there is another 700 million with an average IQ of about 92 (adjusting for what can be termed as Flynn effect). I would estimate that the average IQ of India is around 94