1998 Mazda Protoge- RPM drop really low during idle

Recently, my Protoge will go almost dead when I am sitting in idle. The
RPM's stay right under 1000, but then will drop to about 200, then go
almost dead. Sometimes, the battery and check engine light will flicker
as it is about to die. We recently had it serviced and all the mechanic
could find was the air compressor was broken and i needed new transmission
fluid. Could it be a problem with a fuel filter? Please help! Thank you!

So is the air compressor still broken?
Is the low idle what you took it in for originally or is it running like
this only after you got it back?
I'd think a siezed component like the compressor would bring the whole
engine to a screaching halt or close to it since the engine has to try and
turn the siezed item, but if it came back and is now like this from being
serviced then the guy must have left a vacuum hose off somewhere.

You might want to tell these guys what the mileage is, and when the last
time the filter was changed that you know of.