Here's one I noticed a while ago but only recently started chasing it down.

Car: 2005 6spd Base w/sport package (manual HVAC controls).

Symptoms:
I can hear a click inside and outside the car and the MAF rate will jump about 0.5 g/s. 5-10 seconds later, another click and the MAF rate drops back down. 5-10 seconds later, another click, MAF rate jumps again. Repeat.

It happens when the AC is on or off, including when the entire HVAC system is off.

I disconnected the wire going to the AC compressor and it stopped but this isn't a long term solution.

Anyone else run into this one before?

 

The a compressor will run in every mode (even if you push the button to turn it off) except for front vent and front/floor combo. All others the compressor runs.

Maybe that'll help with your troubleshooting?

 

It runs even when the AC button is off and the HVAC blower is off?

 

I noticed same. I also believe, as above, that it turns on in any mode that includes window vents. So if you put it to just face or just feet, it shouldn't cycle. This makes some sense, you want dry, conditioned air, not wet regular air for your windows. I suspect this is as designed. The fact that it cycles even with the hvac fan at 0 might just be a programming oversight.

 

AC button off, yes. HVAC blower, no.

You sure it's not rad fans cycling?

 

The AC compressor is definitely cycling on/off regardless of any HVAC settings (AC button on/off, any blower output selection from 0 to max, any vent selection). It stops when I unplug the wiring harness from the AC compressor.

 

Try cycling the a/c button. I'm not 100% on this, but feel like I've gotten it to stop by cycling a/c on and off again in a feet/face fan mode.