If you have to keep your foot on the gas to keep it running sounds like the battery voltage is low and the PCM forgets the IAC (Idle Air Control motor)count because of the low voltage which causes the PCM's memory to loose the IAC count. Thats why it wont idle without your foot on the gas. It does not mean it has to be the battery but it sounds like a low voltage problem which could be a bad ground or bad cable if the battery is definetly good. I also recomend doing a voltage drop test on the starter and battery circuit first. Could even be a bad battery cable. Dont let tight grounds fool you as I have seen a few tight grounds have over 8 volts drop through them. Good luck , Ron