Took my MCS03 for MOT today. Cars has 103k on the clock but still drives nicely. While the MOT guy was doing the fast idle test he came over and asked how long the engine management light has been on? Strange - the engine management has never been on while I've owned it (past 2 years). Sure enough whern he shows me, the engine light is on (yellow with small icon of engine on it). It came on while he was testing it! The EML light has not come on. He says it's misfiring and the exhaust does sound like it's misfiring but it drove fine on the way home (35 miles) and doesn't at any point seem to lose power. The engine light is still on (not the EML light).

Anyway car failed on the emissions with them being well over the allowed limit (don't have the fail doc in front of me so can't put the actual figures).

Because of the possible misfire I was thinking it might be the coilpack, HT leads or plugs but would expect the car to run much rougher than it is.

Spose I'll have to get the fault codes read.

Can anyone tell from my description what the problem is likely to be?

Thanks in advance!

Hi ya

It's worth having a look at your airfilter and plugs and leads as you say normaly on the coil pack it's no3 cylinder that rusts up pop of the lead have a look.
It sounds like it my be one of the 02 sensors has gone like you say you need a code reader to See what fault code is.
If one of the sensors are on the way out it will cause rough running and high emissions
If you are a member of the AA or RAC you may be able to get them to pull the code down

Hope this helps

Thanks for the reply Marque.

When I started the car this morning the engine light went off and I'm sure the car is driving fine. If I rev while in idle it sounds fine, no misfiring. When I stop the revs and as the engine slows down I can hear the exhaust 'putting' but it stops as soon as it's idling again - don't know what that means? The natural idle is around 800rpm.

I've looked at all the posts on the coilpack and they were all clean and rust free. No.3 did have the very slightest amount of what I thought was rust but it cleaned straight off with a rag. The ends of the HT leads all looked fine where they connect to the coilpack. Haven't looked at the plug ends yet or the plugs themselves.

Noticed my oil was quite low so have just added a litre.

Here's the figures from the MOT emissions:

1st Fast Idle Test:
CO - 0.00% - PASS
HC - 0 ppm - PASS
Lambda - 2.033 - FAIL

2nd Fast Idle Test:
CO - 0.00% - PASS
HC - 1 ppm - PASS
Lambda - 2.223 - FAIL

Now that the engine light is off, will it still register an error code? I know the light goes off if the problem doesn't happen again after 3 consecutive journeys, which is obviously what's happened here.

I'm going back to the MOT station today to get the emissions tested again. I'll report back with the outcome.

Hi ya

The code may be stored not all codes bring the light on if the pre cat 02 sensor is failing it will cause a rich mixture but will only register a code.
It could be something like a bad water temp sender going out of limit. The WT gauge is only there for cosmetic reasons it's not accurate. I have a scan gauge I use in my car to keep an eye on it also good for seeing the codes and resetting them
Give you car a good thrash before taking it in clear it out abit :-)
I would try to get the car plugged in to a diagnostic tool see if there's any codes stored

Hope it has sorted it's self out :-)

on R56s the light turns off after 3 independent journeys without issues. I guess the error is still recorded.

Slow response, been busy.

Took the MCS back for emissions retest the day after it failed, and it passed no problem this time. As I said the engine management light had gone off by the next day and the car had not misfired at all since the failed test. The only thing I had done is clean the connectors on the coil-pack, although they really weren't particularly dirty. I also took the car for a very fast, 10 mile drive on the M1, immediately before the retest.

The lambda result came in at 1.001 (allowed range is 0.97 - 1.03) so well within the range.

Cars can be such a pain in the butt sometimes but I was thrilled that it didn't cost me anything to resolve (except the petrol from the M1 thrashing).

That's interesting. A lambda over one is lean, under is rich. That lambda suggests you're running an AFR of 30-32:1, which is rediculously lean. I'm thinking you may have had a loose connection. I'd check your O2 sensor as I would be willing to bet that's the code you're throwing. If you were misfiring, you should be rich, not lean. Because your hydrocarbon and carbon monoxide levels are fine, I'd be willing to bet there's nothing actually wrong other than as suggested.

I'm not even sure it was misfiring to be honest. I only have the testers word for that. He came and got me from the waiting area when the engine light came on. He said it was misfiring but it wasn't when I went over. Anyhow, something happened to give that lambda reading and bring the light on. Just going to have to see if it happens again and then investigate the suggestions of sensors further.