The other day I got a hankering to trim down my MAF sensor's post, and after doing some reading decided that doing so would be a mistake. I just want to make sure my primitive understanding of why it would be a bad idea is correct.

What I've pieced together is that the MAF approximates airflow by generating a low-voltage current based on (pressure? conductivity? magic?), and this voltage is sent to the EEC which interprets it and adjusts fuel flow accordingly. Thus, if X amount of air is rushing past the stock MAF's sensor wires, it interprets that as meaning that Y cfm of air is reaching the combustion chamber (where Y is less than X, as the probe post obstructs some of the flow) it will send a voltage signal of Z to the EEC, and calculations are made using that Z variable.

My assumption is that an aftermarket MAF works similarly, with one important difference: the voltage output is increased based on knowing how much more air can flow past the reduced surface area of the MAF's probe. Subsequently, the same X amount of air getting to the actual sensor wires of the MAF will generate a Z + 1 (for the sake of argument) voltage, as it's known that more air will be getting to the combustion chamber due to the reduction of the probe's surface area (so that the actual Y cfm is much closer to the X reading of the probe, or at least greater than the stock Y value would have been--I'll say it's Y + 1 for the aftermarket MAF).

Finally, the problem with simply cutting the excess post off of a stock MAF is that the sensor wires are getting that same X airflow reading as in the above two scenarios, but the Y value of air entering the combustion chamber is much closer to the aftermarket's number of Y + 1. The MAF being stock, however, isn't designed to take this + 1 reaching the combustion chamber into account, so it's still sending the lower Z voltage signal to the EEC (rather than the Z +1 as in the aftermarket MAF). Getting a signal that only Y air is entering the combustion chamber (rather than what's now Y + 1), the EEC doesn't increase fuel delivery and the engine begins to run lean, hence the rough idle and other problems associated with MAF modifications.

Is that anywhere close to being right?

 

Makes sense to me. Unless of course there is a proportionally increased amount of air through the elements. The only time I can see this being a problem would be at higher airflows than stock. I don't think there would be a problem under most driving conditions, and possibly not at higher airflows either.

The maf is a small heated wire, and incoming air cools the wire as the air flows over it. The temperature drop changes resistance of the wires and thus varies the voltage output to correspond with air flow.