Idle goes bad on TQ

I seem to have this recurring problem with the TQs on my LA engines, wherein I'll get it running really nice, with a nice idle, and it passes its smog test with flying colors. Then a couple of weeks or a month later it starts dumping too much fuel into the engine at idle, so it idles too fast and rough. The fuel bowl wells are intact and the engines don't hydrolock, so I think something is wrong with the idle circuit, maybe? Too much of the transfer slot exposed? Any help would be appreciated. Thank you.