when i had the same problem long time ago, I suspect my vaccum switch valve (VSV, or idle up switch) is not working. yun pala mali mali lang kabit ng hose.. ito yung papunta dun sa malapit sa carb na sinasabi mo. when i gave up trying to figure out for myself, dinala ko sa friendly neigborhood talyer sa may amin.. sinilip nung mekaniko yung linya nung vacuum. sabi nya mali mali nga connection.. so he corrected it... done in less than 5 minutes.

So I suspect any good talyer can do the job for you. Kung malapit ka sa cubao, dun sa petron na tabi ng toyota. magaling mekaniko dun. kung may papalitan pyesa, ikaw bibili. Meron parts shop dun sa tapat non petron. I have no idea kung magkano ang vsv. good luck!