Right, lets tackle them one-by-one
When you come off the throttle completely, the ECU should disable the injectors until the engine speed drops to around 800rpm. You should see the Injector Duty Cycle drop to 0% and the Injector Pulse Width drop to 0.000 too, if you're logging via EvoScan. This is perfectly normal, and on a long enough zero-throttle coast, the AFR should lean out as far as your wideband will read. Well, it *should* be doing this, but @
foxdie did set the injectors to come back on at 2000rpm rather than 800rpm in his tuned ROMs - for pops/bangs on overrun - so this may affect what I said above (it certainly did on my Anglia!)
At idle, it *should* be aiming for 14.7, and it should "hunt" either side of this very slightly (14.0-15.4ish, as I've seen on my Anglia)
When you press the accelerator slightly, the engine ingests a sudden gulp of air - this causes the initial leaning out. When under no load, very little fuel is required to maintain that increased engine speed, so it is not surprising to see an AFR of 18.
There is also the response speed of your wideband - some will "smooth" the output over a few samples rather than giving an instantaneous reading - don't forget too that there's the delay in your gauge too - a gauge with a digital readout will always respond quicker than a gauge which has an arm that has to move.
Realistically - AFRs at high load high boost are most important - and 11.5 is absolutely spot on.
Checking for boost leaks is always a very useful diagnostic test - and if you're unsure, perform a boost leak test ASAP!
If the AFR isn't leaning right out on no-throttle coasting, then definitely do the TPS setup procedure to ensure that it's providing the Idle Position signal to the ECU (as a side note, I've never been able to get a value for the Idle Position Switch option in EvoScan, so make sure you use the feeler gauge/multimeter method to adjust it).
The ICV/screw should only be played with if it hunts badly at idle or can't catch the revs dropping away from high RPM (ie if it drops to about 500rpm before recovering to about 670 - it should catch it before it drops below 650).