Real posser here.

[moakesr]

I think you are on to something here.

I had a Vauxhall Senator that exhibited similar problems, surging down the motorway, stalling when coming to halt at junctions etc...

Turned out the lambda sensor was slow, one new sensor later the problem was gone. The diagnostic recommended by Number_Cruncher is perfect for validating if it is the problem.

Good Luck,

Richard

One simple way to look at the lambda sensor is to drive the car with one foot held under the throttle, to keep the throttle absolutely fixed. With a mulimeter on the lambda sensor, see if the surges follow the lambda reading. Holding the throttle fixed should make sure that you don't subconciously correct with your foot.

That the problem only happens when warm might be an indication that it's a closed loop fuelling problem. Again, by driving with a multimeter showing the lambda output you can discount this. From cold start, the lambda sensor will not be switching. The first switch of the lambda sensor is the signal the ECU is waiting for before switching into closed loop mode. If the surging only starts when the lambda starts switching, you're in the right area.

I could well imagine that this is a sluggish lambda sensor, which reacts to changing exhaust gas composition, but too slowly. The two tests mentioned above may go a long way towards either validating or discounting this view.

Good luck - There's a certain extrememly enjoyable satisfaction to sorting a problem which has baffled others!

 

[IanA2]

this is as good as Agatha Christie.....

 

[OzC36]

Engine wiring harness?

 

[Ian B Walker]

Result (ish)

Dear Readers,

Today I achieved a result (at long last):bannana::bannana:. I changed the ERG valve and the Lambda sensor (just for the hell of it). Lo and behold, smooth engine and no surges or sudden stops. Took it for a 10 mile drive and so far, it is behaving (kiss of death statement). Tomorrow I will be able to confirm a 100% result. Keep reading.


Thank you everyone who has offered me advice and things to look for. Without this forum and its members lots of people like me would be lost (including Main Dealers)

 

[grober]

Result!!:bannana: :bannana:

 

[GrahamC230K]

Phew. Now how are we going to divide this bill up?

 

[kth286]

If I may comment regarding the process of fault finding - only change ONE component at a time and then test.

In this thread we do not actually know which changed item fixed the problem, and therefore we have not really learned from the experience (although we have narrowed it down to two items of course).