91 Civic idle

[ukrkoz]

hello

we just bought a 91 civic - $300 - he-he. actually, runs quite well.
it is a MPFI engine.
someone rigged idle mechanically on the throttle by locking the throttle cable. when i had it all untangled, engine stalls. i figured that rpms can be set with an adjustment screw, so i did it for more or less decent rpm number and no stalling.
here's symptoms: engine starts and warms up by itself very well, so the idle control unit obviously works. then, rpms go down to about 800. after some driving, rpms crawl up into 1500 by themselves and have tendency to stay there.
i sprayed carb cleaner around throttle and everywhere close to it, no air is sucked in, as it did not influence rpms at all. i had everything outside throttle cleaned and sprayed cleaner into the throttle yesterday.
my question is: what can cause rpms to crawl up and stay there? i loosened throttle cable completely. cruise cable is loose. will it be idle speed control actuator? that mushroom looking thing with vacuum attached to it? as when i had that vacuum hose removed off it, engine went into some 3000 rpms right away. can it be removed and cleaned inside, like i did many EGR valves before?
appreciate suggestions. not much of a problem, but annoying, plus costs more gas.