1997 Hyundai Sonata starting problems

1997 Hyundai Sonata 4 cyl Front Wheel Drive Automatic

hi, I have a problem starting my car when its cold, I start it then it turns off straight away or I have to press the accelarator when I turn it on to keep the revs up to keep it going, sometimes it wont accelarate when I press the accelartaor and sometimes the revs go up and down and it stalls when I drive sometmes and if im waiting at the traffic lights it starts to shake and turns off, I have taken it to 3 different mechaics, one of them put the tester on it but no problem came up, the other mechanic told me to change the spark plugs and I did and no difference but there was alot of where the spark plugs go so got that cleaned out, can you tell me what the problem is? I cant afford to listen to mechanics that dont know what they are talking about.