A few years ago, i got this bright idea about tweaking the idling rpm on an '89 Corolla XL(1.3L, EE90); i never got around to adjusting it back to the original level.

Flash forward to today, and i noticed that my ride would idle at a very low level, followed by the engine stalling. What's strange is that the problem seems to get worse as i drive longer. Just this morning it stalled 3-4 times. i immediately made adjustments when i got to park, and my idling sits at 950-1000rpm.

So far the stalling problem seems to have been fixed, but i'm just curious as to why the problem came out just now. Is there anything else i should check out?

Turning on the AC engages that thingy(sorry, can't remember what it's called) that pulls the rpm up, but when it disengages it drops to the low rpms i mentioned.

tia