i have a 2002 hyundai sonata, this car has had a multitude of problems, recently the MAF and the idle control valve went out at the same time replaced both with used parts the MAF from a junk yard the other from ebay, however i dont belive their relat5ed becouse i have always had this problem since i replaced the air filter with a cold air intake that i built, origonaly i had one made out of plumbing starting after the MAF howeevr it was soon replaced when i found that the plumbing smelt odd and the pvs pipe was melting (this can release chemicals and let unfilterd air in)my problem is and always had been the car lagging when it takes of, it idles fine but when i slam on the gas it goes slow and ever once and awhile the reves would drop once or twice befor it would finaly go, now after i "fixed" my cold air intake the propblem is far far worce, when i take of (floor it) it will take off like any other car but once it reaches about 2k rpms the reves will constently drop fairly quickly over and over untill the car reaches a speed wheir the idle can get over 2k then it takes off just fine, if i press the gas petal like normal however it accelorates just fine no studdering or anything so i was wondering if the cold air intake was letting in more air than the MAF coould registor and it wasnt getting enough gas in and when i shortend the intake it just made the problem worse or if it was just exposing another problem. (also when the MAF boke i drove for awhile with it unpluged and it drove just fine aside from a few hard shifts so would than mean a gas shortage? or a miscalculation?) any help even guess's would be appriciated.

 

4 months later, still not even a guess

 

Problem: used, junk yard parts and cobbled home-made CAI
Solution: replace with new parts and the factory intake and air box

 

Also check and make sure that with ur homemade cold air setup when the engine torques back the intake hose is not pulling off and allowing extra air in past the maf. Plus, I would never fully trust a junk yard maf, best to get new from factory or swap off another car that you know is good to test.