How to throttle Grequests when making asynchronous API calls?

I am using the grequests library to pass ~250000 urls to get data from an api.

The API has a limit of 100 calls per second.

How do I throttle the grequests to only pass in 100 urls per second? I increased the size parameter from 5 to 100. Not sure what this does but still running to error 'Max retries exceeded'.

Here is my code so far:

import grequests

lst = ['url.com','url2.com']

class Test:
    def __init__(self):
        self.urls = lst

    def exception(self, request, exception):
        print ("Problem: {}: {}".format(request.url, exception))

    def async(self):
        return grequests.map((grequests.get(u) for u in self.urls), exception_handler=self.exception, size=100)

    def collate_responses(self, results):
        return [x.text for x in results]

test = Test()
#here we collect the results returned by the async function
results = test.async()

response_text = test.collate_responses(results)

Grequests seems to make 100 requests and then without any waiting makes another 100 requests and so on. There is no time defined between these requests. Here is a similar problem described with a solution: Limiting/throttling the rate of HTTP requests in GRequests