nismofreak1208

Hi guys,

Awhile back, I posted about p0491 and p0492 codes which I solved when I changed my air filter. Turns out, the hose connecting to the flapper inside the air box was literally ripped off so the codes are appearing due to this. I attempted to trace the line to the secondary air injection pump but I gave up as the lowest temps I see in hawaii is 68 degrees. Is there anyway to use VAGCOM to disable these codes from reappearing? I clear them with a OBD scanner every few days but if I can do a full disable, then that would be great.

Moving on, after I swapped the air filter, I plan to do the cabin filter, coil packs, and plugs. Is there anything else that I can take care of besides the timing belt change?

Also, My 4.2 v8 idles around 750-800 rpms and vibrates noticeably in cabin. When looking at the passenger headrest, you can clearly see it vibrating. Since I am OCD, this bothers me a bit and I was wondering if anyone knew a solution? I thought about swapping the engine mounts but there is no leak or cracks on them to dictate the change. If I hold the idle at 900, the vibration is considerably less and almost non-existent. Should I use VAGCOM to raise or is there possibly something else wrong?

MP4.2+6.0

In general, I suggest you proceed with the tune up. It may get rid of your current vibration issues at the same time.

You need to fix the secondary air injection. That is part of the emissions system, and you can't defeat it--or anything else in the emissions system--with a wave of a VAG COM wand/re code. If your air feed lines are in place, look at the vacuum hoses that drive the combi valves (combination EGR and air injection). Typical system behavior after reset by the way is it runs two cold hot cold cycles before determining readiness. If still screwed up, check engine light goes back on.

You cannot alter the idle speed with VAG COM either. Only do-able via some obscure freeware (maybe; I used it on my C5 A6 4.2), and it takes an old serial (not USB) cable as well. But, even if you did that, it's just an end around to deal with a symptom, not the core problem. That is, of course engine should run smoothly. Thus tune first, and get to bottom of the codes issue too. If still vibrating, suspect motor mounts and/or the front motor torque mount.

nismofreak1208

Is there a schematic photo breakdown of the SAI? I tried to follow where the broken hose went to but once it went alongside the strut housing towards the firewall, I couldn't see anything. I didn't want to try to remove the larger hoses that run along the back of the motor towards the airbox area. The hose that is broken tho is a much smaller almost reinforced plastic type hose. I know it operates the flapper in the airbox to bring warm air from the engine bay into the air box to help warm the engine up faster. I thought about buying vacuum hose until I physically saw this line broken.

MP4.2+6.0

You should get a manual like Bentley.

Audi's have not had a prewarm system for cold air essentially forever, and the concept left American vehicles with demise of carburetors.

What system is doing is pulling air FROM a hose in the air box. It goes to an electrically driven air pump which activates when cold. When it does, pump pulls air from air box and pumps it through the combi valves toward the back of the cylinder heads and in turn that air goes into the exhaust systems before the cats. Fuel system runs rich when cold and that extra air being pumped in helps light off (heat) the cats more quickly. System deactivates after a few minutes from cold start. Meanwhile "combi"(nation) valve "reverses" when hot to assume an EGR function where exhaust gas then flows to intake side to reduce combustion temps and nitrogen oxide production.

Combi valves and the general function and pump have been around since C4/D1 (1990's) so if you search for general info on its function, most any Audi info should explain it.

On your broken hose, yes they need to be sealed and functional. If you have a broken air feed hose, a faulty air pump (rare) or bad vacuum connections to the combi valves, the light will turn on. Air hoses--whether formed rubber or quasi hard plastic are typically dealer only and somewhat pricy. In the past when I have found broken ones I can often patch them temporarily with some oil resistant rubber hose and clamps unless they are broken right at the end connector.

Cars are supposed to have a vacuum hose diagram under hood. You should find parts of the air injection system referenced there, though the diagram focuses more on the vacuum hose elements. On the other hand, from prior postings it seems like some D3s are missing these stickers. A clue the hood may have been replaced or repainted in the past.

nismofreak1208

Would this be the correct bentley manual to purchase?

I'll have to reattempt this weekend to see if I can find the other end to the SAI pump and hope theres still some plastic hose left to do a temp fix with a regular vacuum hose and hose clamps

MP4.2+6.0

You need an old Windows XP computer to run it--it was never updated for later Windows platforms. If you don't have one, maybe a friend has one buried in a closet or box somewhere.

You can also get alldata (alldatadiy.com) via a subscription model. Like $40 for 5 years. Not as comprehensive as Bentley, but okay for many regular things and platform independent.

nismofreak1208

This is an off topic question, but what was the optimum lowering via VAGCOM for our cars? I swear I read 15mm front and 10mm rear is best for day to day driving without sacrificing ground clearance

MP4.2+6.0

so I stopped there. I tried out to 15mm. I'm on factory 20's so probably feel it a little more. Even at 10mm, if I put it in "Dynamic" and am on the freeway, the pavement has to be pretty smooth or the increased harshness becomes apparent. Factory 20's ride about .35" higher than 18's or 19's but also have less fender gap going in, so I am still net riding at the same height as an unmodified non-sport A8 on 18's or 19's. But, my fender gap is also down about .7" overall compared to stock height on 18's or 19's. It all nets to enough drop for me looks wise but preserves ride feel in general.

Sport drop is 20mm factory of course, but only has the last 5mm to go.

Personally I would not want to be lower than I am. If I want to style it, I can always put it in Dynamic. I already find myself engaging lift mode once in a while with tall curbs and parking blocks, and the nose has had a few scrapes with at driveway and intersection gutters/swales. Having dealt with a flooded freeway underpass last week and the occasional snow berm, I already need the clearance I have, even lifting it up on the fly. BTW, if anyone else drives your D3 (wife, GF, kids, etc.), I would be more conservative--they may not take the same care with road related obstructions where clearance matters. Another reason I stopped at 10mm.

nismofreak1208

Hmm, very good points. My wife is the only other driver but she is accustomed to lowered cars as my previous was a 98' static dropped lexus gs400. I was planning to lower as I am thinking about purchasing some vossen cv3 20x10.5 et40 in the future with 275/35/20 tires. Since you are already on 20's and the 10mm seems to have a harsher ride in dynamic, how does 5mm feel in terms of comfort?

ltooz_a6_a8_q7

-I cleaned the throttle butterfly.
-Find all the vacuum hoses connected to the manifold and FI system, chances are you'll find a cracked-leaked-one or even one that wasn't pushed in all the way or loose.
-Make sure all electrical connectors are connected and not hanging without locks due to sloppy mechanics before you.
-Tune up is more like a desperate gunshot way of fixing the problem with a lot of wishing.
-If you're spark plugs are shot - you can't drive smoothly at any RPM.
-I drive with a 4 year old air filter and the idle is still good and smooth - clogged air cleaner is total false cause - especially with dry air cleaner.
-I fixed many rough idle cars and all found dirty throttle body, broken hoses. loose electrical wires.



Cheers and good luck,

Louis
PS: the last tune up was done at the dealer @55k miles - now I have 99,360 miles - bought the iridium spark plugs, was going to replace a few months ago, but the spark plugs were still like new - didn't do it yet - the car still idles perfectly - 45k miles spark plugs still performing - will change on one of some nice days.