Now I've had this problem as of late that the car begins to run rich, buck, and stall when it's well warmed up and either in idle or low RPM ranges for any length of time. Mush research has lead me to consider several possibilities; water thermosensor, air intake temp sensor, FPD, and or FPR. So, I decided to start with the water thermosensor. Unfortunately, this did not solve my problem (though I think it was still a needed job) and I will be moving to the next item on my list. However, I wanted to post a few pics and my experience with the replacement project for those who might need to do the same (because it appears that several owners have similar problems and this did resolve their issues.)

There are three water thermosensors in all, one of them a different part number for automatics, so I went for the one on the backside of the water pump housing. Part number F202-18-84A (No.1). The other two are under the UIM and (looks like) in the fuel rails. Anyway, I started by draining the coolant from the radiator plug (but this doesn't remove all the coolant) and allowed me to pull the pump. I also removed the IC and cross member that the batter tray, airbox, and IC mount to. This I found was necessary to be able to work the pump out later. Pull the belts, alternator, and air pump. I also removed the intake air tubes to make it real easy to reach all six coolant hoses. The upper and lower radiator hoses, and four others from the back and passenger side near turbos. Not easy to reach but workable. (I have to say, this job is really best when engine is out but that wasn't and option for me). You will also need to remove the alternator mounting bracket (the bolt hidden just above the power steering pump was really hard to break loose, 14mm I think) Once the bracket was off and all hoses removed, you can remove the bolts (12mm) that hold the pump on (easy part). But next comes pulling the pump. The oil metering lines run over the lower radiator hose portion of the water pump which I had to get as much slack on as possible. The problem is that the studs that the pump slides on are very long! Be careful when working this part off and not to brake the lines or anything else!
Once off, the sensor is easy. It's located on the back side of the pump housing and just below the thermostat (green plug). $50 was my cost for the thermosensor and it came with the o-ring seal, but, another problem. The black plug and wire that plugs into the sensor broke. The wire was badly corroded and brittle. Fortunately, I was able to use a spade connecter to re-install.
Also, you will need a new pump gasket, part number N386-15-162 and only a few $$, but be sure to completely remove the old one from the front block and pump housing. Otherwise, you will leak coolant when all back together. (I had to scrape it off with a putty knife).
Putting it all back together is easier but again, those oil metering lines are a pain. It's easier to get pump back on but the lines run up and around the pump just below the alternator. It takes some work with a long screwdriver to get them out of the way so you get a clean seal between the front block and pump.
Of course, re-install coolant lines, connections, and hardware. I also had trouble getting my alternator back on because some wire connectors just above the pump don't hide away well. And of course, double check everything to spec before refilling coolant. Also, if you haven't changed coolant in your FD before, it takes time to fill, you might have to work the upper hose like a pump to get it all in, and do your air burping. I found too that it took a few days to get all the air out of the system.
I can’t think of any other details that you might like to know about but ask if you have Q’s. The two pics show the sensor and the oil metering lines and how they run over the pump.
On another note, if someone has a suggestion to help resolve my troubles please speak up.

 

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Umm...I did mine a few months back but didn't pull the water pump or drain from the radiator. IIRC, other than the tower brace and IC tubing, I removed the alternator and just siphoned coolant out of the filler neck until it was below the level of the sensor. It's tight, but definitely do-able w/o pulling the water pump.

 

I don't have a PFC but if I had one I would first look at the 02 sensor voltages, the throttle sensor settings and surely the vacuum readings. I am assuming you can view these via the commander. First off a rich mixture will make a higher voltage (02 voltages range from .10v to around 1 volt or so). Voltages around .8 or .9 is rich and would confirm your view. If the 02 was lower around .2 to .5 that normally means its on the lean side, but when an 02 sensor fails it may read in the lower ranges because its unable to preform correctly and the ECU will add fuel because it sees a need. This will compound the rich problem more. If the voltages are on the low side lets say at idle and you can smell heavy sulfur coming from the exhaust that is a good sign the 02 is skewed. So replace it. What ever your idle vacuum was when it was running good should still be the reading you see now or close to it. Vacuum leaks are common and not always easy to see. Last the throttle sensor should be looked at for proper adjustment. Just some basic things to think about.

 

I have a new O2 sensor, I checked as many of the vac lines as I cood, even pulled the UIM to check sthose, my voltage readings are good and tps is within spec! I did try the easy stuff first.

 

I tried but there was no way I could reach it. Besides, now I have a good seal and electrical connection. It is interesting how some people cand do the same job in different ways but it just wasn't going to work for me this time. It was fun just the same.