Something else is wrong, I know, DUH
The computer sets the idle RPMs using the IAC Valve, this is not like a set screw where its a fix idle
The computer has the RPMs from the crank sensor and has "target idle RPMs" in its memory based on engine temp(ECT sensor)
Cold idle should be about 1,100rpm
As engine warms up idle drops, computer closes IAC valve bit by bit
Warm idle 750rpm, for automatic trans, manual trans is 625 usually
Computer adjusts voltage at IAC Valve to open it and close it, and its accurate +/-3rpm
Which is what I mean by something is wrong, lol.
MAF sensor can certainly cause a bad air/fuel mix, but idle wouldn't change, computer would just open IAC valve a bit more and try to stabilize it at its "target" RPM, computer is very responsive with IAC Valve voltage.
IAC valve gets 12volts on the red wire with Key on
The other wire(White/blue) is the Ground but at the computer(pin 83), computer pulses the ground to lower voltage closing the IAC valve a little at a time
This is a very accurate way to control voltage
If RPMs are dropping to 500 then computer is not controlling IAC valve, maybe bad wire?
You can use sewing needle to pierce the IAC valves wires, then use a volt meter to see the voltage going to IAC valve, with key on, and then engine running, generally 8 to 11volts, lower voltage lower RPMs