O2 sensor or what?

bit long story. maybe stupid but.
was preparing car for nct. was in garage to check emissions before go to test centre. it was bad. was guessed somewhere vacuum or exhaust leak. fixed exhaust, rechecked(some was replaced) vacuum pipes. go there for second time. still was bad but not to bad. blame was gone to BOV. replaced BOV. and go there third time emissions was very good(it was Tuesday).
after two days(Thursday) go to NCT. emissions was way too far from good. even on idle speed. in garage idle speed emissions was bad just first time.
NCT told me that could be O2 or cat. for cat nearly 100% sure its good.

and now funny story. today did memory read(black connector connected) no faults. did dynamic test for faults(green connector connected). showed up faults 32 O2 sensor. cleaned O2 sensor connector. tried clear memory( black and green connectors connected) again showed O2 sensor. but when was reading memory(black connector) it didn't show any faults. again tried clear memory(black and green connectors connected) in the end showed that memory cleared and no faults.

will go check emissions again to garage today. but it could be that O2 sensor playing stupid games? did memory reading would show O2 sensor faults or just in dynamic test mode(just green connector connected) it will show up?

PS might be one more thing. in garage emissions was checked with turbo timer on in NCT turbo timer was off.

Turbo timer should have no bearing on emmissions, intermittant fault on O2 sensor maybe? The sensor could be just starting to go?
What car is it? Could you get a loan of a sensor thats working to fault find the problem?

car is 95 JDM impreza wrx.

in same way just thought engine was washed in thursday morning maybe this could be issue?

[quote author=Federal link=topic=33207.msg380567#msg380567 date=1328881509]
bit long story. maybe stupid but.
was preparing car for nct. was in garage to check emissions before go to test centre. it was bad. was guessed somewhere vacuum or exhaust leak. fixed exhaust, rechecked(some was replaced) vacuum pipes. go there for second time. still was bad but not to bad. blame was gone to BOV. replaced BOV. and go there third time emissions was very good(it was Tuesday).
after two days(Thursday) go to NCT. emissions was way too far from good. even on idle speed. in garage idle speed emissions was bad just first time.
NCT told me that could be O2 or cat. for cat nearly 100% sure its good.

and now funny story. today did memory read(black connector connected) no faults. did dynamic test for faults(green connector connected). showed up faults 32 O2 sensor. cleaned O2 sensor connector. tried clear memory( black and green connectors connected) again showed O2 sensor. but when was reading memory(black connector) it didn't show any faults. again tried clear memory(black and green connectors connected) in the end showed that memory cleared and no faults.

will go check emissions again to garage today. but it could be that O2 sensor playing stupid games? did memory reading would show O2 sensor faults or just in dynamic test mode(just green connector connected) it will show up?

PS might be one more thing. in garage emissions was checked with turbo timer on in NCT turbo timer was off.
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How do you do these live connector tests? I have a few problems with NCT emissions failures myself that i have been trying to diagnose for months and can't get a solution from anywhere yet. I suspected O2 sensor but not getting any fault codes when connecting using OBDII to laptop...
Are there any traders / mechanics on here that are able to diagnose/fix NCT emissions problems?

i can show you tomorow if you want and around dublin.
o2 sensor expensive thing just changed today mine

[quote author=Federal link=topic=33207.msg384395#msg384395 date=1330993686]
i can show you tomorow if you want and around dublin.
o2 sensor expensive thing just changed today mine
[/quote]

yes sure if you're around. i work in city center on ushers quays so car is in here all day until after 5 then i drive home through ballyfermot if that is handier for you. i'd like to get another opinion on state of o2 sensor...

tomorow i will be all day till 6.00pm(maybe bit later) in garage near dog trust on n2 road. you can come.
text me before you go 0860464391

ps what car you have?