I have a 2002 Sonata, 4cyl, 2.4l, DOHC, AC, Auto Trans. When I turn the key the engine will kick over and start, but die immediately if I do not keep my foot on the gas. After 3 or 4 tries the car will idle, usually around 1200. If I put on the AC or put the car in gear the rpm will drop to about 850. Twice I have taken it for a long test drive and it seemed fine. However when I get back, and the starting problem will come back and not go away for quite some time (hours). During that time if I start it up, and hold constant pressure on the gas, the rpms will fluctuate from 500 up to 2500. This all while not increasing or decreasing pressure on the gas petal. If I let off the gas the car will die. I've replaced the air filter already. Could this be a MAF?

 

Look at the PCV hose for collapse and large split/hole in it.. You'll need to remove top cover to see hose, look closer to where it fit to intake plenum... semi common problem..

 

I replaced the PCV and all 4 plugs when I first started to have this problem. I'll check the hose again. Do you think it could be a vacuum problem? Thanks..