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p0172 could be a few issues, A poor performing O2 sensor can cause a rich condition. Also an injector sticking open can cause a rich condition. I would start with a throttle body cleaning and a top engine clean (I love Sea foam) it has the least side effects, run the injector cleaning ( IT MAY SMOKE OUT THE EXHAUST LARGE CLOUDS) dont be alarmed. This is a good thing. Wait a day or so to clear the codes, because the top engine clean may very well set a code anyways.
There is a switch that works the computer upon turning on the air conditioning. Upon turning the AC on the switch sends a signal to the computer to increase the RPM's to the engine so it will not die out
any leaks in intake or exhaust upstream of the sensors, sparkplug
condition and engine controls/sensors for out of range operation
(including fuel pressure and condition of regulator)
IAC should be cleaned and checked as this can cause poor idle and shut
down. I'm not saying not to change O2 sensors, but unless everything
else if OK, it probably won't help.
I don't know how handy you are, but check plug condition, distributor condition and plug wires. Is it running smoothly when it does run or is it running rough at all speeds. Check the fuel filters - probably due for a change anyway.
Could need a throttle body cleaning, air mass meter, various other expensive items. So don't guess, but get a good diagnosis from someone who knows these cars.
Also, check battery cables for tightness, check the ground cable at the block for tightness, check the injection system fuse located on the driver's side front fender. Could have moisture in it that causes injectors to act up. Pull the fuse, look for wetness. If any shows, put electrical lube on the fuse tabs and then reinsert the fuse.