Rough idle on warm start.

[graynada]

Thanks for the reply, I will check again for vacuum leaks again. I have replaced the front pipe that goes not that long ago.

But I have run from cold while monitoring the lambdas and the idle is fine when open loop and then I have seen activity start on both lambdas, and before it gets to 'mid warm' and the idle is still fine also. So it does not seem related to either open or closed loop, however it only happens under closed loop at a certain temperature.

Originally Posted by ainarssems

You cannot discount them. While lambdas are warming up engine runs on open loop. Once lambdas warm up it runs on closed loop based on lambda feedback.

So if you have vacuum leak it might be running lean before lambdas kick in. If You have faulty maf it could be lean or rich before lambdas star working.
And if it is very lean lambdas might never start to show activity.

Check vacuum leaks first

[graynada]

I forgot to say in the original post, I serviced my car 10 days ago, oil, oil filter air filter and spark plugs all changed. My old spark plugs were all a normal colour, no signs of anything sinister there. Since the service there is no discernable change in this issue.

Anybody any ideas on how air flow is controlled at idle?

[david@a8parts]

On the back of the throttle body there is an idle control valve which controls the flow of air past the throttle flap at idle. We have spoken to a few people where this has failed resulting in rough, erratic idling but it does show up in diagnostics usually. We do have them in stock, and it is possible to swap without too much hassle. There is also a thottle position sensor whcih caused a problem on an 8 we had a couple of years back which tells the engine ECU where abouts the throttle flap is. When fully closed it sends the message 'idle' so if for some reason this has given up the ghost or needs adjusting you would also have some similar issues.

Hope that helps, and if you would like deailed instructions on these two items send us an email to enquiry@a8parts.co.uk.

[graynada]

Thank you for the information. I shall have a look at those 2 and see whats what

Originally Posted by david@a8parts

On the back of the throttle body there is an idle control valve which controls the flow of air past the throttle flap at idle. We have spoken to a few people where this has failed resulting in rough, erratic idling but it does show up in diagnostics usually. We do have them in stock, and it is possible to swap without too much hassle. There is also a thottle position sensor whcih caused a problem on an 8 we had a couple of years back which tells the engine ECU where abouts the throttle flap is. When fully closed it sends the message 'idle' so if for some reason this has given up the ghost or needs adjusting you would also have some similar issues.

Hope that helps, and if you would like deailed instructions on these two items send us an email to enquiry@a8parts.co.uk.

[graynada]

OK this has developed into MoT failure on emissions My results were (pass mark in brackets)

1st fast idle - CO % Vol 2.53 (0.30) HC ppm Vol 70 (200) Lambda 0.93 (0.97/1.03)
2nd fast idle - CO % Vol 2.37 (0.30) HC ppm Vol 72 (200) Lambda 0.93 (0.97/1.03)
Natural idle - CO % Vol 2.15 (0.50)

They too suggested a vacuum leak. I have inspected every hose I can get to and been spraying carb cleaner to try and find a leak but to no avail so far. The lambdas are providing so weird responses. Sometimes they are switching as you would expect, sometimes flat lining, and sometimes a steady 0.5ish volts. I have attached a log of them from an around town drive.

I found a valve that is clicking at a very fast rate, picture attached. Does anyone know what this is? Something to do with tank venting?

On the other side of the car there is a vacuum tube that appears to be heading aft. Any one know where that ends up?

I am assuming you have to take the plenum off to get to the 3 hoses on the back of the block mentioned in Audipages? If I take the plenum off can the seals an gaskets be reused or should I get some in ready before I start?

Any help would be greatly appreciated, I getting no where fast and running out of ideas

I seem to be struggling with the attachments so I'll try those in a separate post

[graynada]

Uploads not working for me

The valve is near the 2 ignition 'amplifiers'. Vacuum hose in either end and a 2 pin plug. Unsurprisingly when I disconnect the plug it stops clicking but this had no affect on the weird lambda readings

[ainarssems]

That is running rich. Cannot be vacuum leak in intake as that would cause lean running. Most likely bad lambdas or air leak in exhaust near lambdas causing them to have false readings.


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