Poor idle quality - Help & advice please.

[Rusty]

Not sure for how long this has been going on now but while the idle has held steady, there's a definite lumpy nature to it

• I've had the infamous 561 fault code for a while that's been coming and going but a recent discovery of a small leak in the exhaust pre-lambda *may* address that one. There are no other codes.
• I've swapped the MAF over for another and the fault has remained the same.
• I've disconnected each injector in turn with a similar change in idle for all 5.
• I've checked the spark plugs and they seemed fine but i'll check them again.
• I've checked all 5 boots - they were new one but I could swap them for the old ones, which were in working condition when removed.
• There is no oil in the the spark plug holes, thanks to a new rocker cover gasket.
• I've cleaned the ISV with no change.
• I've done a boost leak test with no leaks.
• The breather is fully custom and leak free.
• TPS idle switch is being operated.
• Throttle cable has 1 notch of slack when the TB is in idle position.

There must be 101 other things, so please post them up.

The symptoms of the fault are that the idle is slightly lumpy with a slight cough on the exhaust.

What is the measuring block for the MAF check? I can't use the measuring blocks but can do a single block measurement.

TIA for any help

[Monkeymagic]

if it helps rusty mine seems to change pitch ever so slightly on warm idle the revs don't fluctuate but the exhaust move defiantly does slightly. as the car runs well passed its emissions etc i assumed it was normal or me being to twitch

[Rusty]

It's never been silky smooth but it's definitely a bit more juddery than before while not wandering all over the place or having any cause which is obvious to me

[GazzaG60]

test the tps also.

[UrS4boy]

...The symptoms of the fault are that the idle is slightly lumpy with a slight cough on the exhaust.

Either an ignition issue (replace your sparkplugs - try the 3 point Bosch FR5DTC tri-electrode spark plugs that EFI Express suggests) or you have a burnt/bent valve that is preventing as much compression (and efficient detonation) as the other cylinders. You should do a compression test to confirm or eliminate this possibility: http://forums.quattroworld.com/s4s6/msgs/174154.phtml



Photo courtesy of EFI Express

[Rusty]

Cheers chaps

The talk of valves reminds me that I have new lifters to fit due to one being a bit sticky when giving some beef, so there's a possibility that the offending lifter isn't operating properly, although I've not had any of the tap tap tapping recently... Might be an idea to get them swapped for the nice new ones I have.

TPS idle switch is definitely clicking on/off, this was something that I checked (I'll add this to the original thread). I also adjusted the throttle cable to give a little more slack in the system, as it was hair-trigger sharp but this made no difference.

I'll check throttle angle using VAG Com at some point soon but I didn't see anything today in a cursory glance through the available measuring blocks.

Will also do a compression test when I swap out the spark plug boots and maybe plugs. The plugs that are in there are not that old (fitted at the same time as the boots, when I rebuilt the coil pack wiring) and are some Audi branded F5DPORs that were purchased a few years ago.

That reminds me, I did have a misfire under high load some 18 months ago, due to the coil pack wiring being shafted (I rebuilt it) but there is none of this - it seems to run well on WOT, although 'seeming to' and 'actually doing' are often a hair's width apart

[twoqu]

Another member with the 00561:

http://www.s2forum.com/forum/showthread.php?t=62598

One thing I think you have in common is an aftermarket downpipe. I have noticed that the boss seems rather deep but there does not seem to be conclusive evidence that the position of the probe alters the reading significantly. Just an observation!

[Rusty]

My lambda has moved a litte further down the pipe. I could put it about 2" from the turbine exit but was going to use this for the EGT probe...

[twoqu]

Don't you both have the same downpipe?:

http://www.s2forum.com/forum/showpost.php?p=469978&postcount=113

It may just be a coincidence. I was more concerned with the depth of the probe in the exhaust stream. The boss for the lambda seems quite deep.

[dobbin]

my isv valve was leaking causing tickover issues i glued the back of the valve with
2 part eppoxy resin

[Rusty]

Don't you both have the same dowmpipe?:

http://www.s2forum.com/forum/showpost.php?p=469978&postcount=113

It may just be a coincidence. I was more concerned with the depth of the probe in the exhaust stream. The boss for the lambda seems quite deep.

Technically, yes but in reality, mine was the prototype and has subsequently been modified to fit the Wagner EM and my Lambda is just after the first bend.

I agree that the picture shows quite a tall boss and will take a look at my DP and see what sort of boss is on there

[ericd]

you tried playing/wiggling with the maf plug connector and see has any noticeable effect on the idle ?

[Rusty]

I'll have a looksee...

[mcandmar]

If were talking rough running at idle/low revs i would start with a compression test, then check for vacuum leaks (specifically around the injectors). Often overlooked is the injectors themselves, by 100k miles they really could do with a proper clean. Or if you have a 7A just bin them!

[Rusty]

Injector clean is a good call. They're in good condition visually but that has no bearing on the spray pattern...

Vac leaks would be shown up on the boost leak test, as I o the whole system.

Compression test is now on the to do list.