MOT Fail on Idle and 2nd Fast Idle

[as400]

BMW Z3 2.8 failed on both...does the garage have to carry out a CAT test having failed the BET?

[Pica-Pica]

as400 said:

BMW Z3 2.8 failed on both...does the garage have to carry out a CAT test having failed the BET?

I shall follow this thread. My wife’s Fabia has just passed its MOT, but the readings were approaching the top end (Car is 11 years old, 83k miles 1.2 TSi petrol).

[VTC]

as400 said:

BMW Z3 2.8 failed on both...does the garage have to carry out a CAT test having failed the BET?

the failures I have ever had on my sons car were always down to exhaust leaks, maybe worth checking exhaust condition firstly.
if unrelated to your issue never mind

[trickywoo]

With those lambda readings I’d be checking the o2 sensor.

[paintman]

Look for a hole in your exhaust downstream of the lambda.

[Mad Maximus]

I don’t understand the emissions tests but my old e39 Failed a couple of times on emmsions and I used cataclean both times and worked like a charm to get it passed.

[Athlon]

No temp reading, no rpm reading, poor test.

It's rich on those readings for sure though

Edit to say yes, if a car fails the BET we set the machine up for a full test using the specific data for the make and model. Some BMW's had crazy lambda numbers that passed (lean burn)

Edited by Athlon on Monday 4th March 21:29

[Kuwahara]

Athlon said:

No temp reading, no rpm reading, poor test.

It's rich on those readings for sure though

Edit to say yes, if a car fails the BET we set the machine up for a full test using the specific data for the make and model. Some BMW's had crazy lambda numbers that passed (lean burn)

Edited by Athlon on Monday 4th March 21:29

I had a nightmare with an E91 I had a few years back at MOT time on the second fast idle ,the mechanic who I’ve known for years and is very capable was at his wits end that the numbers were miles off.

Turns out the guy doing the test had put in the wrong engine code(tbf there was a change to lean burn at the time) so a simple mistake.

Had a dig on a BMW forum and it was a common issue on this engine 318i, once the correct code was entered it sailed through…

[as400]

Not sure how the emissions machines they use work...I see my Z3 was entered as E36 3 series...is that right?

[stevemcs]

you should have had that tested next week then you wouldn't have lost a months MOT.

Is it on fresh fuel, when was the oil last changed, it doesn't show any exhaust leaks on the failure which is normally a contributing factor. Is it getting warm ? As mentioned they bypassed the temp and just looked at the water temp, first test is normally oil temp 60deg, then 80deg if it fails first time

[as400]

stevemcs said:

you should have had that tested next week then you wouldn't have lost a months MOT.

Is it on fresh fuel, when was the oil last changed, it doesn't show any exhaust leaks on the failure which is normally a contributing factor. Is it getting warm ? As mentioned they bypassed the temp and just looked at the water temp, first test is normally oil temp 60deg, then 80deg if it fails first time

Reasonably fresh fuel (within the last 2 months), major service 6 months ago, some have suggested replacing the lambda sensor(s) but it says Pass on both Lambda lines so is that necessary?

Very possibly it may benefit from a good run before hand, thing is you drive to the garage switch off and it starts cooling immediately so still not sure what the temperature would be when they come round to test.

Annoying that last year it passed and was nowhere near failing on emissions.

[trickywoo]

as400 said:

Pass on both Lambda lines so is that necessary?

Lambda should be 1.00 or a fraction out. Although a pass your readings suggest an issue. If it’s not a leak the o2 sensor could well be at fault.

[stevemcs]

as400 said:

Reasonably fresh fuel (within the last 2 months), major service 6 months ago, some have suggested replacing the lambda sensor(s) but it says Pass on both Lambda lines so is that necessary?

Very possibly it may benefit from a good run before hand, thing is you drive to the garage switch off and it starts cooling immediately so still not sure what the temperature would be when they come round to test.

Annoying that last year it passed and was nowhere near failing on emissions.

Just make sure they retest the emissions after you have given it a bit of a drive, there is an extended test when they fail on emissions.

[as400]

...and one faulty O2 sensor replaced...all is good! thanks.