General Lambda Sensor

[croftside]

Hi, My Panda Selecta Auto has just failed the MOT, as they could not complete the emission test, apparently the revs were going up and down on tickover and they could not get a proper reading. They said it was probably the Lambda sensor in the exhaust system, that was faulty. I just wondered if anyone else had this problem, before I go and spend more money on something that may not be the cause!!. Any comments would be greatly appreciated.
Geof

 

[petel]

Ask on the Punto section, the engine and system are basically the same as the Punto 55. Someone will have seen the problem before. It may be the Lambda but it could also be a connection, a failed ECU reset or the throttle body.

Don't be side-tracked by the fact that it is a Selecta, the problem is with the engine and the engine neither knows nor cares whether it is attached to a manual or an auto box.

Presumably you were aware of the fluctuating revs situation before you put the car in for MOT?

Please let us know how you get on, there are several Panda Selecta owners on here.
Rgds.

 

[oldernowiser]

Generally if you have a lambda sensor problem you get a warning light on the dash (the exception being early 1993 versions with Bosch fuel injection and _no_ warning light).

To help cure your varying idle speed, I'd try the following things - in no particular order:

clean the inside of the throttle body and edges of the butterfly valve with some carburettor cleaner (or brake cleaner) and a _lint free_ cloth.

reset the ECU - especially if you've performed the step above

take the car for a spirited drive down a dual carriageway or motorway to blow the carp out.

measure the fuel pressure presented to the injector.

check for (air)leaks in the inlet manifold and associated pipework (including MAP (or vacuum advance depending on who made the fuel injection system) and brake servo pipes).

check you have good ignition leads (and plugs)


[ramble]
old lamdba sensors get a bit sluggish responding to the changes in exhaust gas, and this will cause the light to come on at steady high speed, and _might_ cause varying idle speed.

The confusion with a sluggish sensor is that you can see the thing switching (if you look at the lambdas voltage with an oscilloscope or suitable daignostic tools), but still have problems.
[/ramble]

 

[Most Easterly Pandas]

[ramble]
old lamdba sensors get a bit sluggish responding to the changes in exhaust gas, and this will cause the light to come on at steady high speed, and _might_ cause varying idle speed.

The confusion with a sluggish sensor is that you can see the thing switching (if you look at the lambdas voltage with an oscilloscope or suitable daignostic tools), but still have problems.
[/ramble]

SNAP! This is exactly what happens to my Selecta at a steady high speed (55MPH+)

So is it anything to worry about, and should I change the sensor?

It also hesitates sometimes on acceleration. Would this also be linked?

 

[Most Easterly Pandas]

the revs were going up and down on tickover

What was engine temp? I doubt it was a really cold start, But my Selecta does this for about 30 sec after start up on a cold morning (2 Centigrade and colder)