my car had this kind of problem before, so what i did was go to kedai potong get myself a good TB with good condition isc motor, my car is 4g15 injection but i bought myself a 4g63 TB(RM250),throttle response increased significantly not to mention reduction in FC. but still after two years, the ISC melted again so since i can't upgrade to even bigger TB, i just went to workshop and installed an additional toyota ficd, it cost me just rm150 including labour and now the probelm is fully solved.
throttle body problem