NCT test - Emissions fail

t_man

Car is a 1995 Seat Cordoba, 1.4L petrol, nearly 170k miles.

The car was in for test yesterday, and failed on CO emissions for both low and high idle. The values were similar at both idles, 2.89% at low, and 3.03% at high idle. Lambda was also low at 0.91.

HC value at low idle is 235ppm (NA for test for this car), and at high is 175ppm (above 200ppm is a fail). So it's passed, but may be an indication where it's going wrong.

4 years ago it failed on high idle CO, lambda sensor was changed then and car tested fine after that. The emissions were fine 2 years ago. The HC value 4 years ago when it failed was 140ppm, still a pass then, but looking over other NCT reports for the car, it's typically been below 60ppm, for example when the lambda sensor was replaced, the HC value went from 140ppm to 56ppm.

Other details:

Air filter changed maybe 6 months ago (during summer).
Spark plugs, leads, distributer cap and rotor arm changed Oct 2008.
Catalytic converter is original.

New exhaust backbox installed in September 2012. About a month ago, I noticed some excess noise, and saw that the exhaust was escaping at the new joint, and that was fixed about a fortnight ago, by fixed I mean the mechanic reseated the connection, and used some grey stuff to seal it.

Fuel economy seems to be fine, I did a few long journeys over the christmas break, and it's about the same as it was 10 years ago (100 miles approx per 1/4 tank).

Car drives fine, responds when it's asked to, no excess smoke, and isn't burning oil (oil level hasn't changed much since September, and approx 3k miles ago). It can sound a bit "throaty" if I floor it, but I only notice that if there is a hedge or concrete divide right beside the car to hear the echo.

Another thing to note, back in October there were 2 days (Sat and the following Mon) when the car was hard to start. I ended up taking off the distributer cap and cleaning the contacts with WD40, leaving it for a few minutes, and it started fine after that, although it was running rough for a few seconds (maybe 3 or 4 seconds), before it settled down to running smoothly. Car has started fine every time since then.

Anyone have any suggestions as to where to start, what is likely to be wrong with it? I was thinking of replacing the spark plugs leads and distributer cap and rotor at the least first, and taking it from there, but what else might be going wrong here? If the catalytic converter was past it's prime, would the CO values be so similarly high?

Appreciate any helpful suggestions/comments. Thanks.

t_man

I was having a look at the engine this morning, and was looking around the air box on top of the engine, and the vacuum pipe that comes out from under the air filter box, to the air inlet pipe, it was clipped to the underside of the plastic air box, but when I unclipped it, the pipe came out very easily.

I took off the air box, and saw where the pipe is supposed to go, put it all back together, clipped the pipe back in place, and now when unclipped, the pipe doesn't come out with the same force as it first did (when I unclipped it the first time, it literally just came out from under the air box without any force it seems).

The vacuum pipe seems to be involved in opening/closing a valve between fresh air, and air from where the exhaust comes out of the engine. Is this just hot air from that shroud, or is it recycled exhaust from the engine?

If that vacuum pipe wasn't on properly, could this be a cause of the bad emissions?

Or what other symptoms would I have noticed if the pipe wasn't on correctly?