allenst

Hi. Do you know if one of these manuals posted will deal with cleaning of the Idle Air Valve (is that it's proper name for the 04 A8L)

If it not too tricky I'd like to clean it as I've read it can become sticky of a little clogged with time and therefore might be why I'm getting stuck at 1000rpm while coasting to a stop or feel a little resistance as I accelerate through 1000rpm.
It's more noticable on coasting. It can stay at 1000rpm for 100meters then will slowly fall through 1000rpm.
(changing MAF did fix shudder and flickering needle but the stickness at 1000rpm still somehwat exists)

haggisuk

Anything to do with the engine is in the bfm manual, if it's mechanical, fuel manual also has relevant info and electrical manual also.

But the ignition manual covers injection and ignition and may be more to your needs, but it's worth studying all of these in spare time to give a good overall understanding of how each system interacts with each other

dvs_dave

Reading through the various SSP documents is time well spent if you're serious about understanding how the various systems work and diagnosing problems, however they are not repair manuals.

For info there is no separate idle control valve like engines back in the day. Idle speed is controlled by the ECU by fine modulation of the fuel injection and electronic throttle body. Clean your throttle body, check its functioning smoothly and swiftly, and all is well recalibrating it and see how you get on.

MP4.2+6.0

Idle air valve? Seriously? Please quote the materials you are looking at. I bet it wasn't "the manual" I keep mentioning... Sounds like more wild goose chase internet surfing to be blunt. Here I will bother to say exactly why. I kind of doubt like other posts you may not respond on point here either, but oh well.

I had one in my Audi so know exactly the part. It was probably the one that actually caused the run away Audis "like on TV." Only problem was...it was a 1985 Audi 5000 with CIS-E. That is, if you call it the integrated function with the idle stabilizer. From 1975 with the C1 100LS and CIS (mechanical) injection until 1984 with the C2's and then the first year of the C3's (5000S/100), they actually used a distinct "idle air valve." In 1985 it got integrated with that new idle stabilizer component. It was used essentially like a choke to trick the air plate into thinking more air was running past it and increase the fuel flow at idle. really yesteryear stuff, and all pre electronic. I also know from first person work on them, back when it was mechanical and with no diagnostic tools like VCDS. My mom's 75 100LS with first year CIS--now 40 years ago...--was where I first ran into the part. Sat right under the air cleaner bolted to the top of the injection manifold. If you need more diagnostics from 1975 to 1984... Found a picture by surfing myself; see below. It's right in the center. Notice the distributor cap, wires and cast iron block; it even has an apparent knock sensor so it is "newer."

Since you mention MAF, the only other logical thing in there is the throttle body. Just pull off boot and use some cleaner if you are worried about that. You have been poking around similar symptoms for many months and posts as I recall. Maybe long time to get it to a professional indy/garage? Wild goose chases and internet surfing to me. Or we can keep pretending about a manual, at least for a car from post-millennium.

allenst

ok thanks.
I have read on and off the manuals but honestly it can be beyond me at times ! shocker eh !

Why I asked about idle air valve is that the 04 A8L started to drive with a fluttering needle and some shudder right after I removed the battery.
This wiped the ECU but I did check the throttle with vcds and it was ok but perhaps I used vcds incorrectly, or I needed to drive cycle first, or other--before measuring the throttle using vcds.

I had read that the ecu had 'learned' to employ the throttle even with errors I had but now that it was wiped it could not 'learn' and therefore my fault MAF was exposed. I changed MAF sensor and the sdudder and flickering needle are gone. All that is left is this resistance to breaking as I coast and come down to 1000rpm. at 1000rpm needle stops and I can feel car continue to drive, not accelerate, but just kind of hold at 1000rpm. It can do this for 100meters before falling on its own.
For this last issue I had read brake booster, Idle Air Control Valve as most likely causes.
So I asked about the Air valve.
Again, car did not behave this way before battery unplugged so I am not convinced my torque converter suddly started to act up and I had checked ATF level and it was ok.

allenst

thanks Smily
look the only repair I can't learn or handle would be dropping the tranny
so I am going over everything but that.
you yourself made a llong list of possibilities.
I am working through the possibilities.
the MAF did correct most. I still need to check to see if it fixed my lean codes.
I do suspect more than 1 vacuum leak....that's a wild goose chase if nothing visual jumps out
...and, I like to tinker around the boards and see how people are solving certain issues.

haggisuk

I wasn't sure what you were talking about, but its becoming clearer, you have a issue with the revs staying higher than idle which is effectively pulling the car that bit harder?

The car has the ability to monitor many sensors to determine if the fuelling is correct and if need be adjust things to get it as close to perfect as it can.

There are Long term fuel trims and short term fuel trims.

The long term ones generally adjust over a long period of time to compensate for wear etc.

Short term is done on the fly as you drive.

If there are leaks in your intake system the car will to a point try to compensate for it by adjusting how much fuel gets squirted for each combustion cycle. If it goes beyond the scope of adjusting to compensate you will get a warning light and fault codes to go with it.

Getting back to the dragging throttle, I sounds like and correct me if I am wrong that you replaced the MAF recently but not done a throttle body alignment?

If that's the case then you ought to do one, I will put a link at the end of this reply please read it and pay attention to the requirements before doing it.

When you get the vcds cable be sure to save a scan straight out , clear all dtc's scan and save again. then carry out the TBA ONLY if you have no fault codes in the engine.

Throttle Body Alignment (TBA) - Ross-Tech Wiki

allenst

thank you.
I did have the Bank 1 and Bank 2 lean codes. changed maf but dont have a scan tool right now.
I believe the SAI to be causing some issue and probably a vacuum leak.

let me try to characterise the "1000rpm" issue.

when taking off from stop it 'fights' a little to get through 1000rpm--yes like a lag--but that resistance only lasts until I get to 1200rpm and everything goes to normal.

the inverse happens on the way down whil coming to a stop.
as I come down to 1000rpm I feel a push back by the brake or let's say like the car is getting gas on it's own so it can stay at 1000rpm.

so resistance on way up through and resistance on way through down the 1000rpm mark.

all other driving conditions now seem normal other than that point on the dial.

so the ecu thinks something needs to happen at that point other than what is actually happening. that's what led me to query about brake booster, throttle and the Idle Air Control (which this model does not have) and any other fuel delivery issue that might cause this condition.

dvs_dave

Ok, how to fix your problem(s):

1. Buy VCDS. Literally pointless continuing on without
2. Buy ElsaWin manuals for $15 off ebay
3. Listen to what we're telling you rather than just endlessly shotgun guessing about what it might be.
4. SAI has nothing to do with idle or vacuum control either. It's purely for emissions during warm up and essentially just blows air direct into the exhaust to speed up cat light off.
5. New MAF will very likely give strange throttle responses at low throttle openings as it's compensated over time to accommodate previously bad MAF.
6. System doesn't know MAF has been replaced so you need to re calibrate it by doing a throttle body alignment as detailed above.
7. Do all this and then report back to us.

MP4.2+6.0

Add to the list one I increasingly wonder about:

for allenst (OP), what exactly is the situation on general tune up maintenance? When was the last basic plug set and air filter change? I don't remember you mentioning routine maintenance, and you didn't answer the recent timing belt interval question I posed in the coolant change post. Bottom line, if you haven't done the basic tune up, that's of course like first up as you proceed.

for dvs_dave, the one place the SAI could cross over here is the vacuum line to the combi valve that runs the EGR hot and the SAI system cut over cold. That is, assuming the set up remains the same as my A6 C5 4.2. In my experience with both that vehicle and the prior 2.8 A6 I had with SAI and combi's, the area behind the heads where combi valves live (at least one) gets really hot and tends to cause vacuum lines to deteriorate. Another one of the parts (combi valves) I really don't miss with the somewhat different W12 set up. Agreed with your and other responses the MAF really needs to be adapted when replaced.