Co idle changing

Just had a juke back at the mot results to 2015,, 0.010 0.050 0.010 0.030 and 0.030,, normally I would have done the engine service before the test but not since 2015... normally about june or july, I am wondering if the fluctuations in the readings are an indication of the engines health or will a service before the next test bring it back down to 0.010.
 
can be all sorts, I always give it a good 15 mile motorway run before an MOT so it's fully hot all the way to the exhaust tip, and then rev the b*llox off it a bit when I get near the test centre to blow out any cobwebs

Things to check if it fails would be: air filter, injectors, o2 sensor, EVAP (if your car has one), spark plugs and make sure you don't have any codes because some of them will cause the ECU to play with the air/fuel mixture
 
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