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Running Rich at Idle


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Hello Gang,

I have a 2001 Land Rover Discovery 2 gas engine with about 140k miles I took it to get it tested for emission ( smog ) its a requirement here in California to renew registration and it failed the guy said its running too rich at idle.

Here is the test result maybe someone can recognize what could be wrong.

GAS Reading

HC..........PPM: 394 ( he said it needs to be 70 )

CO.............%: 4.60 ( he said it needs to be .5 )

CO2...........%: 8.2

O2.............%: 6.4

P.E.F ............: 0.469

If anyone had any idea what could be wrong please let me know your help will be greatly appreciated.



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I would agree with Bogmonster, sounds very much like the Hego sensors are faulty but it could also mean your cat is knacked, also check normal things like air filter isn't clogged and all the spark plugs are ok

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With a Co reading that high you can forget the cats for now,its much more likely one or both of the upstream oxygen sensors failing to switch up rich,(0.8v) so the Motronic Ecu will keeping widening the pulse width of the injectors to try to see a rich signal.As you car is NAS spec it ought to have downstream sensors too,these monitor cat efficiency and really ought to be putting the check engine lamp on.Am I right in thinking there are car parts stores in the US that will read OBD codes for little or no cost ? This would be a good stat if you can as the codes that Motronic logs are usually very accurate.You could read/note/clear them and drive 20 miles,then read them again.Running this rich the codes will quickly log again.Just remember failing leads/plugs will cause a misfire that is almost impossible to detect - these will give high readings too if the Oxy sensors are OK. The plugs/leads work VERY hard on these cars and need to be in top order.Finding a garage that makes regular use of an Oscilliscope would be good as faults can be pinpointed very quickly this way.

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So can you give us figures for a stable 2500 rpm - reason I say this is twofold,first is because at this speed the exhaust gases will be hot enough to "light" the Cats,this will reduce the emissions even if the engine is running continually rich .Secondly if one or both of the heating elements in the upstream oxygen sensors is not heating at this speed the sensors will be hot enough to start switching and give useful info to the ecu for proper closed loop fuelling.

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