Search is your friend they say. And I found some threads touching this issue but nothing that completly solves my problems. With that said "I'm sorry for MAYBE doing a double post"

Now to my Issues.
I installed a Innovate MTX-L Wideband last year at this time. Took out the old OEM Lambda and just popped this new Bosch into the existing bung in the downpipe. MTX-L Narrowband output goes to blue? wire on OEM lambda loom and Wideband 0-5V loggingwire goes to ECU.
All was fine, MTX-L performing good numbers 14,7 @ Idle and 10.3 (about) AFR @ WOT. In December last year I noticed that once in a while @ startup with warm engine Idle AFR wasn't 14,7 anymore rather 15,8 AFR. But a quick dip on the throttle brought it back to 14,7 AFR again.

Now when I doing a Cold start in the morning when the car's been standing overnight AFR rises from around 11 AFR to 14,7 and stays there (Open Loop, right?) BUT every time I do a Warm Start (between 10min to 4h after last use) I get a AFR reading of 17 and it stays there... ALWAYS... If I don't touch the throttle AFR stays @ about same reading. Fluctuating between 16,6 - 17 AFR. If I dip the throttle and keep revs above 3500rpm for just a second AFR reading comes down back to normal 14.7 but jumps around between 14,1 - 15 AFR.

When I driving my car normally (cruise) AFR reading fluctuates between 13,2 - 17,5. @ WOT I get a AFR reading of 11.2 (about)

Have checked for air leaks, found nothing. Did a Exhaust test earlier this week. Lambda was spot on 1.005 CO = 0.18% O2 = 0.4 HC=128

What could be causing this rather odd behaviour? Faulty Lambda sensor? It have been calibrated regularly 4 months apart and 3 times this week.
I have Evoscan but I'm rather noob to that Software. Did a small log when the car was in my garage the other day.