Sir,
I would suggest Liqui Molly EFI Cleaner, have seen these stp brand bottles but did not trust them. LM is a german company and well know brand i have used its EFI and Carb Cleaner for a dozen times on different cars results are brilliant with no side effects. One was my coure which i kept for 3 years and now my friend has it.
It would cost you 700 Rs for a 600 ML bottle pour it in fuel tank in about 10 Ltrs of fuel and let it do its work. While you are at it do check Engine Flush also by LM its price is 510 rs.
Do share the results