Hi all,

My Mpi Seicento has covered 40K and is fine when started up from cold but after about 10s the engine "Judders" slightly while idling.
I have not had it long and its done it since I got it.
Its had a "Big" fiat main dealer service ( filter, plugs etc ) and at the same time the crank shaft sensor was changed as I was having problems with it cutting out.

Reading the various threads on Lambda sensors it seems that they last about 40K and various people seem to experience things running smoother when fitting a new one.

The Mpi appears to have two lambdas , one pre and one post cat.
I removed the post cat lambda ( being the most accessable ) and it had a slight whitish deposit. I gave it a squirt of carb cleaner, cleaned it up, and tried things again. The judder is about the same.

I also have a Gendan Engine check interface so I took a look at the trace / peaks of the two Lambdas. When comparing the two one is defintely showing a better response than the other. At times the more sluggish one levels out for a bit and then starts peaking / falling again.

- Would you expect to see a similar response for both the pre and post Lamdas?
- Do you think the lambda could be causing the judder while idling?

post cat lambda should have a much lower output. If its not, it means the cat is failing but this would put the engine check light on.

You can phyically swap the two lambdas around if you like. Cleaning them rarely does anything though apart from more damage.

I have got a new Lambda on order.
When I get it I'll try it post and pre cat and compare its response trace.
I'll let you now how I get on

I replaced the pre-cat lambda with the new one.

The response trace seemed to improve very slightly, it did run far more sweet even though a slight judder remained ( although improved )
I have also changed the ignition lead set for good measure.
Finally I disconnected the battery overnight to to reset the ECU.

All seems much better.
:yum: