Technical emissions failure

[weezie]

HELP! i took my car for mot today and it failed on emissions, one of the reading was a pass on the first reading and a failure when it was done a second time.
this was the readings

oil temp 84 pass
first test fail
rpm 2618 pass
CO 0.556 FAIL
HC 238 FAIL
LAMBDA 0.989

SECOND TEST
RPM 2424 PASS
CO 0.437 FAIL
HC 99 PASS
LAMBDA 1.068 FAIL

NATURAL IDLE TEST
RPM 765 PASS
CO 0.275 PASS
OVERALL FAIL
Does this make sense to anyone as to what it could be, the car is going in on monday to possibly find out,
the car is a fiat punto grande 1.2 x reg

 

[richie.guy]

Can't be a grande on an X reg...you sure it's not a Mk2?

Routine question is when was it last serviced, i.e. sparks and leads?

Lambda sensors are the next port of call.

 

[NumanR]

Second test shows the emissions were coming down, if the car gets driven gently then it could just be a catalytic converter not working properly due to internal temperature not being reached. Catalytic converters get lazy if not heated regularly up to correct temperatures, if you do lots of short trips, or have the vehicle sitting for days on end without being used this allows deposits to coat the cat internally and reduce its effectiveness. You need to thrash the car for half an hour to fully heat everything in the exhaust, (lambda sensor will get heated through at the same time), this will make sure the cat has its best chance of being able to reduce the emissions to within spec. If you have a multimeter you can then check your lambda sensor signal output, the signal should oscillate between 0.1 volt and 0.9 volts completing a cycle at least 1 time a second at 3000 rpm.

 

[pk090]

Take it for a thrash bottle of redex in the tank and clean or new air filter