OK so MOT failed today due to CO emissions during natural idle but appeared to be fine during fast idle. Any help appreciated at this time need to get back on the road ASAP and cannot figure out what could cause this. Everything I have seen online shows CO fail at both natural and fast idle speeds.
Measurements
Engine Oil Temp --- Min 60 Deg C --- Actual Value 60 Deg C --- OK
Fast Idle Test
Engine Speed --- 2500-3000rpm --- Manual Check --- PASS
CO --- <=0.200% --- 0.101% --- PASS
HC --- <=0.200% --- 75ppm --- PASS
Lambda --- 0.970-1.030 --- 0,998 --- PASS
Natural Idle Test
Engine Speed --- 450-1500rpm --- Manual Check --- PASS
CO --- <=0.300% --- 0.807% --- FAIL
Measurements
Engine Oil Temp --- Min 60 Deg C --- Actual Value 60 Deg C --- OK
Fast Idle Test
Engine Speed --- 2500-3000rpm --- Manual Check --- PASS
CO --- <=0.200% --- 0.101% --- PASS
HC --- <=0.200% --- 75ppm --- PASS
Lambda --- 0.970-1.030 --- 0,998 --- PASS
Natural Idle Test
Engine Speed --- 450-1500rpm --- Manual Check --- PASS
CO --- <=0.300% --- 0.807% --- FAIL