My GF has a 01' Elantra and I can't seem to fix the sputtering. I have changed the spark plugs and oil. It overheated once and I've changed coolant and thermostat. Cleaned map and TPS sensor. Cleaned throttle body. No check engine light is on. It does it in the morning when car is cold and also on up hills. Anyone have any ideas? I also have thrown some sea foam in the gas tank... No luck. Please help.