Fiesta 1.4L MK6 high CO

Mates Fiesta Flame 1.4L FXJ engine has failed MOT.
High idle 1 CO 0.38 (0.2 limit) HC 74 ppm (200 limit) Lambda 0.996 (0.97 - 1.03)
FAIL
Hige idle 2 CO 0.15 HC 51 Lambda 1.004 Pass
Nat Idle CO 1.11 (0.3 limit) FAIL
Was told he needed a new cat £300 and they might damage the 02 sensors +£100.
Front O2 sensor reads near 0.9V at idle and cycles 0.1V 0.9V at high idle.
Rear O2 sensor 0.4v cold. Rises slowly when held at very fast idle 4000rpm to >0.8v. Drops rapidly to about 0.1v when throttle snapped shut and then c limbs slowly back to >0.08V. Is this slow response and initial bias correct ?
The car is rarely used outside 30/40 limits and owner drives nicely. Last M -way trip was Xmas. The "Italian tune-up" is no longer an option as the MOT expired last week.
Car had a misfire problem about 2 years ago, had to replace plugs and coil.
(using google groups as not at home)
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On 25/03/2018 13:56, Peter Hill wrote:

first Q. was it fully hot when tested? if so, does the ecu know the correct engine coolant temperature?
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On Sunday, 25 March 2018 14:50:25 UTC+1, MrCheerful wrote:

sors +£100.

le.

rpm to >0.8v. Drops rapidly to about 0.1v when throttle snapped shut and th en climbs slowly back to >0.08V. Is this slow response and initial bias cor rect?

st M-way trip was Xmas. The "Italian tune-up" is no longer an option as the MOT expired last week.

oil.

I have no idea about test condition as (they always do) they by-passed all checks "engine temp showed warm" but it does that when still quite cool.
I got coolant up over 80deg C (forscan and torque) to get response from rea r sensor.
No lambda/cat related codes stored.
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On 25/03/2018 14:57, Peter Hill wrote:

I would get a second test done and be sure it is actually hot. Also check there are no exhaust blows anywhere as that can throw things out.
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