"By praising Modi for specific things, we help frame public expectation of his continued behaviour and raise the bar against which we will judge him in future," said Tharoor in his letter to All India Congress Committee (AICC) Communication Department chairman Ajay Maken.
Earlier , Tharoor defended himself for his remarks on Modi where he showered praises on the new Prime Minister.
"I think the problem with our media is that it misrepresents what it reads very hastily or doesn't read at all or it is reading paraphrases of my article. What I said was Mr Modi is trying to rebrand himself and remake himself from a hate figure to an avatar of modernity and progress,"Tharoor was quoted as saying by CNN-IBN.
"From May 16, we have nothing but positive accommodative inclusive language of reconciliation. We have not heard Hindutva being mentioned, we have not heard a divisive rhetoric. But the moment Modi says or does something divisive or sectarian, the Congress party will oppose it," he said.
Tharoor said it would be 'churlish' not to acknowledge Modi's attempts to reach out to all.
Tharoor told NDTV, "We have been extremely concerned about what Mr Modi represents and his aspirations and ambitions on coming to Delhi. What has been a pleasant surprise for the likes of me is the way in which he has actually conducted himself and spoken after his election."
"From the moment of his victory, he has been amazingly gracious and accommodating particularly in the language he has said and the tone he has used, I think it would be churlish not to acknowledge for example when he says that he would be PM for everyone, including those who have not voted for him, that he would like to serve all Indians," he said.
Tharoor said he should not be called a "Modi fan."
The Congress MP grabbed headlines after he praised Modi recently.
In a article in the Huffington Post, titled How Narendra Modi May Have Evolved into 'Modi 2.0' , Tharoor said: "In the event, Modi overcame this negative perception, re-branding himself as an apostle of development and pointing to his successful record in Gujarat, a state of high growth rates that under his leadership has been a magnet for investors."