Erratic Idle

[chash360]

When doing routine checks I have forgotten to re-hook up the MAF plug before and it behaves exactly like you describe, reving up then dropping, almost dying then rev up, on and on..... I suspect that a faulty MAF sensor would also cause this same behavior. It is also possible that its only partially plugged in causing it to not throw a code, the manipulation of getting the airfilter back in and clamped can easily unseat the plug. Best check is to unplug it completely, start the car, note any changes in operation, turn off, then plug it in firmly again, to see if that clears the problem. (I never rely on a computer to tell me the problem, it can point you in the right direction but they are not a replacement for real trouble shooting). If the behavior is different with it unplugged you may have another issue, if it is exactly the same and it does not clear up after plugging it back in fully, suspect your MAF wiring or the sensor itself. Look for physical obsrtuction in the sensor too. A pine needle in the wrong place can foul up the readings without throwing a code. The O2 sensor can also have affects here (but slower reacting) as the 2 are working together to optimize your mixture.