Wow, what did I do?

[austent]

2000 ML 320; it has been a relatively trouble free ownership. It went into 'limp' mode, got it home. I took off the positive battery cable and let it sit for about 15 minutes, thinking it would reset and I could get to the local Autozone for a code reading. I tried to start it and it first went to erratic idle, surging and died, then it goes to idle and dies immediately. Advice? is there a code reading tool I can buy for future use? David