find out which cylinder is missing. when its screwing up at itle pull the plug wires. swap spark plugs from good cylinder to bad. get a stetoscope and listen for injector click. check corosion on injector harnes its fairly common. i woudl also measure resistance on the injector. should be around 13ohms. it wont tell you if its good or bad but will give you a better idea of its condition. tap on the maf at idle with a screw driver handle and see if it acts up. check intake piping for holes or cracks around teh Throttle body. at certain rpm it may allow extra unmetered air to enter the engine and if maf does not know about it it will as you said fall on its face.