2000 VW Golf 2.0 misfires 30 seconds after start

My car is a 2000 VW Golf GLS, 2.0, automatic.  My problem is this: Car starts right up always, idles and revs normal, after 30 seconds runs rough and bogs when revved.  Does not go back to normal until you turn key off and restart, at which point it repeats the misfiring after 30 seconds.  I say misfire because that's what the codes said.  The 3 codes pulled where cyilinder #1 misfire, Cylinder #3 misfire, and multiple misfires read.  I replaced upstream O2 sensor and Crank pos sensor and no change.  Coolant temp sensor recently changed but don't see why that would be an issue since car does it when hot or cold.  fresh plugs.  i'm thinking low fuel pressure, coils, or MAF??  Any thoughts appreciated.  Why does car "reset" itself each time key is turned back on or off?