spoon2000

The engine on my 2000 A6 4.2 surges repeatedly for about 20 seconds after a cold/morning start. My check engine light is on, and the codes are P1411 and P1423, both having to do with the "AIR system."

Any thoughts on what/where the problem might be?

Thanks in advance.

MP4.2+6.0

As usual, vacuum lines to start

spoon2000

I poked around a bit, and at first glance the vacuum lines look OK. I will check more.

FWIW the MAF sensor waws replaced approximately a year ago.

Also, the intake manifold changover diaphragm on the driver's side (which actuates on the passenger's side manifold) seems to be stuck in the sucked-down position (my evidence is the dirt on the valve, the fact that it's still down after the car has been hot, and the fact that it doesn't return to the expanded position when the vacuum tube is removed). It's a bit odd, because when it's down like that it's working against the the force of the spring on the engine block. I understand the sucked-down position is where it's supposed to be on a cold start, so I wouldn't think that would be related to the surging, but maybe I'm wrong.

MP4.2+6.0

Vac lines--look especially at the line along the drivers side valve cover (under the dsecorative center cover). Also look especially at the two lines that drop down the back of the motor and head to some vacuum valves--you pretty much have to remove the intake up to the throttle body for those, and even then, it's more by feel than sight. Those take a lot of heat from below, so if you haven't changed them, expect they are bad. If you are seeing the OEM cloth hose covered hose (the giveway sign it is probably factory original) on a now 7 year old car, no brainer to change it all. My 2000 4.2 started going 2 1/2 years and 30,000 miles in. By five years anything original left was crumbling to junk. Best just to change it all--15 feet does it.

Not aware manifold changes on start up. Idle kick up done electronically as far as I know--remember it's drive by wire so the ECU can just tweak the throttle opening and richen the mixture. Manifold change over shouldn't occur until at least 3000 RPM AFAIK, thus much lower RPM warm up idle speeds should be irrelevant to it. Check functioning the backyard mechanic way by having someone rev the engine in Park to 3-4000 RPM and look for vacuum valve movement. Or the seat of the pants way is drive it--on mine if you floor it in second by 4000 RPM you feel a definite push in your back as the final short tract switch over occurs--kind of like the afterburner kicks in. On a regular 4.2 it is 3 stage, so there are two different transition points; the first is at a lower RPM as I recall.

Expect that part of the motor to be dirty too over the years--road grime comes in around the hood latch area. Thus I don't think any ordinary looking dirt on a valve means much.

spoon2000

Thank you so much for the amazing detail! I will see what I can find! I have had air hoses crack and/or come loose previously so I wouldn't be surprised to find that another one's gone south.

FWIW I noticed the functioning diaphragm sucked in immediately when I cold started this morning, but the one that seems permanently sucked in didn't move. The reason I mentioned the dirt pattern on the diaphragms is that the one that's functioning is clean (as if sucking in and going out has caused the dirt to come off of the rubber part) but the one right next to it that seems stuck in the sucked in position has a thick layer if dust/grime on it.

Again, thanks for the thoughtful input.

spoon2000

After removing the the part of the air intake duct between the airbox and the engine, I discovered that the hose from the air pump that goes to what I think is a kombi valve (shiny silver thing with a top about the size of a soda can) had cracked and come completely off.

Also, there's a cloth-wrapped (i.e. probably original) small hose about the size of a pencil going to the same general area (perhaps to the same valve) that has cracked and come undone, but I can't see where to put it back on.

Local dealer quoted $141 for the hose coming from the air pump. It's either part 077133817B or 077133889 (I forget which). Is it possible for me to fabricate this hose on my own (granted, without all the molded-in angles) from bulk air/liquid hose I'd get at the hardware store?

And does anyone know where the other hose goes? MP4.2+6.0 mentioned getting about 15 feet of hose and replacing all the lines that are similar -- where's a good source for this hose?

Again, I'm grateful for the input as I've already saved a ton of $$$ by doing some self diagnosis thanks to MP4.2+6.0's help.

spoon2000

Went to hardware store and bought a foot of dishwasher drain hose, which has almost the same inside diameter as the original hose. Hose clamped one end to the pipe at the back of the engine, made a splice with the other end to the existing hose using a thin-wall but stiff piece of polysomethingsomething tubing on the inside (so the hose clamps have something to grab and don't crush the outside hose).

Discovered that the pencil-size hose probably goes to the kombi valve, so I stuck it on there.

Went for a test drive, and the car seems to have a lot more pep. The true test will be tomorrow morning when the engine is cold.

I can confirm that the changover valve on the passenger side is stuck. It can be moved by hand but it's difficult, even though the spring is retracting. It's not the fault of the diaphragm, because I can see it's under suction (but not moving) when the engine is running. If someone can advise what position it's better to be stuck in, I'd appreciate it. The one that's functioning properly is definitely sucked in as soon as the car starts, and when the car is hot it stays sucked in.

Thought?

MP4.2+6.0

Standard small hose spec (yes the one about pencil thickness) is 3.5 mm inside diameter. Find something close in high quality rubber on a reel at NAPA or other better parts store, for example Gates or similar known brand. Again 15 feet does the whole motor with a foot or two to spare. If hoses hove fallen off, use the vacuum hose routing diagram sticker under the hood--over near the driver's side hinge--to help trace where each goes. Sticker also names the parts the hoses attach to.

blau parts and ecs also sell it if you want to mail order it.

spoon2000

Sooooo helpful -- can't thank you enough!

spoon2000

<center><img src="http://pictureposter.audiworld.com/66527/p1020903.jpg"></center><p>Pictures of the repair attached showing the new dishwasher drain hose on the right side spliced to what's left of the original air hose on the left. You can also see the inner tubing I inserted to there would be something to bridge the splice. When the pieces are in their finished state, the two black hoses are together.

http://pictureposter.audiworld.com/66527/p1020903.jpg

and

http://pictureposter.audiworld.com/66527/p1020902.jpg<ul><li><a href="http://pictureposter.audiworld.com/66527/p1020902.jpg">http://pictureposter.audiworld.com/66527/p1020902.jpg</a></li></ul>