Turns out that the two codes I got - one for low freq for the MAF and one for the Evap purge solenoid - were both caused by a blown fuse 12 (in the fuse box on the front passenger side under the front brace). Once I saw that both were on the same circuit, I know that was the problem...and it was.
Why the fuse blew is another matter. It was a self inflicted wound. I didn't like the fact that the radiator fan doesn't come on until 230 so I wired in a Flexalite adjustable thermal switch from the radiator into the fuse box to the fan relay. My problem arose when I misread the wiring diagram. I know that the two-wire thermal switch feeds the PCM, which in turn powers the relay. However, I mistakenly thought that the two wire switch was a positive fed resistor, like most two-wire thermal switches are. You know, positive voltage in and increasingly positive voltage out as temp increases. Well, it's not. It's a negative in and out.
With this wiring mistake, every time the fan went on I shorted fuse 12 and the car ran poorly - hard to start and hunting idle. Once I figured this out, I ran ground-in to the adjustable switch and then onto the fan relay (brown wire) and everything works great. I cleared all the codes and the car runs just fine. I used my scanner to set the fan to come on when the engine coolant hits 200. Now I can sit in traffic on a hot day forever (tried this out today in some Memorial Day traffic) and the engine never gets above 200.
Thanks to everyone who posted and all the helpful advice.
This is a great board.
Boatman.
