Hopefully you guys can help me out here again.. I'm going crazy and want to blow this car up.

I'm close to reaching 200k miles with this car.. Recently had a set of fuel injectors go out (5 & 6).

I replaced those, but new problems arose from (I guess) me running on only 5 cylinders for quite an extended period of time. These problems are kind of difficult to explain because of their intermittent nature...

Two days ago, after replacing fuel injector on cylinder 5, I was back up and running on all 6.. but there was a hiccup occurring, I had pretty major hesitation on acceleration from a complete stop, smelled like it was running rich, and had a pretty rough idle. I thought it could be a couple things, so I replaced a couple vacuum hoses that run to the IAC, sprayed my MAF sensor with some MAF cleaner, cleaned by TB, and replaced the distributor cap and rotor.

After doing these things, I start it up and she starts purring just right.. sitting at 800 RPM, pulls away nicely.. I'm happy, though I can still hear a slight hiccup, which sounds (and I'm not familiar with sounds) like a random loss of compression or misfire. This hiccup doesn't seem to affect power (I'm sure it does, but it's not noticeable to me).

I'm happy with it. I put it away; start it up in the morning and it starts searching for idle at around 1k-1.5k RPM, it's idling pretty rough.. I push on the gas a little to get it to about 2 RPM and it smooths out (except for the "misfire" that seems to have no pattern at all). I let off the gas, and it goes back to searching.

Here is the thing.. sometimes it does this, and sometimes it will idle and purr just fine. The hesitation on acceleration from a stop seems to come and go as it pleases as well. I'll be driving from stop light to stop light, and as I sit, the idle will either turn rough (which then facilitates the hesitation), or it will idle and pull away just fine. It still smells like it is running way too rich, also.

This seems to be more pronounced on cooler/wet days.

I did a mode 3 diagnosis on the ECM, and the only code I was able to pull was one red flash, three green flashes (13, right?).. Which I've been told is a Engine Coolant Temperature Sensor.So I started the car and fiddled with the sensor, and every time I push in on it, the radiator fans kick on.. I release it, the fans turn off.I guess I need to replace it anyway, but does an ECT replacement sound like it would fix my problems?

Also,

Would the engine thermostat be playing a role in somehow not allowing the ECT to read the correct temperature, because of restriction of coolant??Sorry if this is an ignorant question.. I'm new at this engine stuff.

It does seem like I have a coolant leak though.. The radiator stays full, but my coolant overflow tank (? whatever it's called) seems to lose coolant relatively quickly but after it gets to about the "Minimum" level, it seems to stop.Could it be leaking coolant from the ECT?