yeh i've found this out too (the hard way)
i was changing my filters over and i forgot to plug the afm back on started the car n it was ideling like shit i thot oh my god wat did i do??? i didnt think it wud be the afm not for 1sec coz i thot the car wudnt start but yeh i looked around and found that the afm wasnt plugged in i got so relieved wen it started idelling good.. phheww