Part II
At this point all there is to do with the FIT valve that's within your capabilities is to check that the plunger inside the FITV thermostat is working properly, and if possible replace with a new plunger.
1. First let the engine cool down, then disconnect the coolant hoses attached to the FITV:
2. There are 3 10mm bolts holding the FITV in place (note I used a mirror so you can see them from underneath):
3. Remove the FITV from the TB:
4. Remove the FITV thermostat housing (held down by 2 phillips screws), be careful not to tear the O ring inside:
5. You should see the thermostat (brass piece) and the springloaded valve recessed inside against the plunger:
6. Now here's the fun part, get a lighter and hold it on the thermostat for about a minute:
7. While looking into the chamber where the plunger is, you should see it slowly pushing the valve closed as it heats up:
I happened to have a spare FITV from another manifold so I was able to swap plunger/thermostat assemblies, I had to swap the plungers as opposed to the whole FITV because the configuration of hoses and bolt pattern was different, but the thermostat/plunger is the same...
8. Unscrew the the thermostat/plunger assembly from the donor FITV with large pliers or arc joint, take care not to damage the assembly too much as it is made from brass (you don't want brass floating around your cooling system):
Compare both plungers. In my case the old plunger was leaking the heat reacting fluid thus not having enough of it to expand and push the plunger all the way out to close the valve completely:
9. Screw the 'new' thermostat/plunger in and tighten with the pliers.
10. Reinstall everything back in and check for suction after the engine is warmed up, you shouldn't have any.
If after all of this you still have suction from the FITV (after engine is warm) you're SOL and need a new FIT valve. If this fixed your FITV but not your erratic idle then you may need a new IACV. Good Luck!
~THE END~