CO reading failed MOT

[bobbybo]

Failed MOT on emissions for CO , Fast idle Max % CO 0.30% reading was 1.24%
2nd fast dile max 0.30% reading was 1.31% so showing more CO when warmer

This Hyundai has only done 38k miles and is a great work car, as its 2001 I need to decide how much cash is worth throwing at it. I stalled it at lights and started a bit hard about a year agop and the enegine warning light came on, then got a scanner and found out it was the O2/lambda sensor reading so changed both sensors with cheapies from fleabay which worked about a week, the sensors are almost £100 each for genuine motor factor ones and may need a CAT too? for that high emissions reading, problem is if i spend that and it is something else underlying like obscure electrical fault its too much for an old car..

shame as its still low miles and runs great

any ideas where to look first or how to isolate the most likely suspect based on readings?

cheers

[bobbybo]

thanks for replies, will replace the CAT sensor and give it a blast then feedback the reading on Monday I have ten days grace on the MOT

replies much appreciated!

[bobbybo]

got a proper NGK front (CAT) O2 sensor from motor factors for £60 and replaced the cheap sh#t one from ebay, MOT emmissions went to perfect, Lambda reading 1 and CO reading 0

keep away from fleabay sensors folks!

thanks again for help