Rough idle on warm start.

graynada · #1 5th March 2012, 06:28 PM

When the car is warm, ie the temperature gauge is between the stop and 90C, my car idles really roughly. If I am stationary for more than a couple of minutes then the CAT light flashes. This is noticeable from a cold start and having driven about 3 miles or when the returning to the car after a short stop.

When the car is up to normal temperature it is fine. When it is stone cold it is fine. Under any throttle it is fine.

For this reason I have discounted vacuum leaks, dodgy MAF as I guess these would not be so temperature dependent. When pull the codes it is always both lambda sensors showing no activity and random misfires; however I suspect this is symptom rather than the cause.

Can anyone give me any pointers where to start?

From previous marque engines I have worked on I would be thinking of cleaning the Idle Air Control Valve. How does this engine (ABZ) control air flow at idle?

Thanks in advance

ainarssems · #2 5th March 2012, 06:58 PM

Quote:

For this reason I have discounted vacuum leaks, dodgy MAF as I guess these would not be so temperature dependent. When pull the codes it is always both lambda sensors showing no activity and random misfires; however I suspect this is symptom rather than the cause.

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 · #3 5th March 2012, 07:23 PM

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.

Quote:

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 · #4 7th March 2012, 06:18 AM

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 · #5 7th March 2012, 06:59 AM

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 · #6 7th March 2012, 07:05 AM

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

Quote:

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 · #7 11th March 2012, 12:36 PM

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 · #8 11th March 2012, 12:40 PM

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 · #9 11th March 2012, 12:48 PM

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.

Check the extensions of attachments are supported. You might want to zip them and the post here if not supported.

graynada · #10 11th March 2012, 12:57 PM

Thanks for the reply.

The exhaust was picked up for a leak on the front (of 3) box although this is not too near the lambda. While we are on the exhaust I only really get it blowing out of one pipe at the back. Could I have a blockage that is upsetting the lambdas, bearing in mind both play up and I have no discernible loss of power?

The files I am trying to up load are of a correct type and well under the 10Mb limit. The error message I get is:

http://forum.a8parts.co.uk/newattach...anageattach&p=

There seems to be a problem on this server.

If loading does not finish properly, please stop the request and re-submit the form.

I could email them if that would help