Santro LE Zipplus 2002, self acceleration proble

Hi, I bought Hyundai Santro LE zipplus in oct 2002. Have done no alterations of any kind. I drive at least 1000 km every month in and around bangalore in all seasons. There is a peculiar problem with my car more frequent in hot weather conditions. The engine gets auto accelerated to its upper limits even when i release the accelerator, and it keeps in that high pitch when i hold down the cluth pedal. If i am still on the move controlling the speed with difficulty, it makes puffing zerks and comes to a total halt and accelerator pedal looses its purpose. I observe lot of heat accumulating under the bonnet. I stop the vehicle and resume journey after some 10 times. I have shown to many hyundai service centers, but they do hopeless investigation and make weird fixes like sensor lines, pedal related, wiring etc.... and bill me a ransom. The problem will reappear after I drive as usual on my normal work day in arid conditions. I am fed up with the level of expertise/interest shown by the service center. I have now decided to show it to a stree side mechanic. GOD BLESS ME and my SANTRO.