some days my friend was having a few problem with his 1999 vitz so i recommended him to remove Cat converter that made a noticable difference in the performance then cleaned out the maf sensor and throttle body that too made a huge difference in the performance,now his car became perfect and was excellent on petrol but was not satisfactory on cng,then we went to a cng shop named cng 2000 and he took about half an hour to adjust the settings and resetting advancer several times but was unsuccessful then came to the conclusion that the advancer is faulty and needs to be replaced but my friend being a computer engineer is a bit more technical in electronic circuits etc.
so as the last resort he took his car to his home took out the advancer,sprayed WD-40 on it thoroughly,left it to dry for the whole night and next day started his car and u know what the car was responsing perfectly on cng even with a/c.so he saved thousands of his rupees by just giving it a thought and was successful!
so i thought to share it with u guys it might be of some help for you people!