aTOMic

so I will look for a defective vacuum hose momentarily. Hope it's the one to the airbox flap...

P1130 , P1128 (fuel trim, system too lean, intermittent). one is bank 1 other is bank 2.

I just wondered if anyone has found other weak points on the vacuum hoses or had a similar experience. Been STFA for an hour or more...


I found the Ross-tech page with " Add" means additive trim, which is addressing an imbalance at idle. When the ECU is using additive trim, it is telling the injectors to stay open a fixed amount longer or shorter. The malfunction (e.g. vacuum leak) becomes less significant as RPM increase. For additive adaptation values, the injection timing is changed by a fixed amount. This value is not dependent on the basic injection timing.

"Mult" mean multiplicative trim, which is addressing an imbalance at all engine speeds. The malfunction (e.g. clogged injector) becomes more severe at increased RPM. For multiplicative adaptation values, there is a percentage change in injection timing. This change is dependent on the basic injection timing.

You can check your current state of trim by using VAG-COM or equivalent to look in Group 032 (in many modern ECU's, consult your Factory Repair Manual for the specific group for your particular vehicle) in your engine measuring blocks. The first two fields will have percentages. The first field tells the fuel trim at idle (Additive). The second field tells the fuel trim at elevated engine speeds (Multiplicative). Negative values indicate that the engine is running too rich and oxygen sensor control is therefore making it more lean by reducing the amount of time that the injectors are open. Positive values indicate that the engine is running too lean and oxygen sensor control is therefore making it richer by increasing the amount of time that the injectors are open.

It is totally normal for both the first and second fields to be something other than zero. In fact, zeros IN BOTH FIELDS indicates that either you just cleared codes (which will reset fuel trim values) or something isn't working properly. If values get too far away from zero, it will cause a DTC (fault code) and can set off the MIL (commonly referred to as the Check Engine Light, or CEL). Specifications for normal operation are usually somewhere near +/- 10%.

In general, an out-of-spec value in the first field (Additive) indicates a vacuum leak since it is mostly present at idle, when vacuum is highest. An out-of-spec value in the second field (Multiplicative) indicates a fault at higher RPM, and may point to a faulty MAF.

Here's a good sanity check for the status of your MAF. Do a full-throttle run all the way to redline in a single gear (second works fine). Group 002 usually shows air mass in g/s (in many modern ECU's, consult your Factory Repair Manual for the specific group for your particular vehicle). Your peak airflow should be roughly 0.80 times your horsepower if you are close to sea level. So, if you have a stock 150 hp 1.8T, expect around 120 g/s. If you see significantly less than that, you MAF may be on the way out. Also note that airflow will be markedly different at higher altitudes due to reduced ambient air pressure, especially with naturally aspirated engines that do not have forced induction to overcome that deficiency.

so that should help.
TIA,
Tom

MN-A8

Try checking the check valves that go to the brake booster. The other day when I hoped in my car after it was sitting outside for a few hours the brake pedal was hard until the engine started. Normally the pedal should stay soft unless pushed a bunch of times. A few days later I got the codes you are talking about.

Still haven't had time to dig into it yet.

jakematic

No other codes in the Auto-Scan ?

MP4.2+6.0

If you see those generalized lean codes, especially across banks, look for intake side issues. And look for those--rather than MAF stuff or 02 sensors--if you aren't seeing other codes pointing at those other components. Thus, look at the big rubber clamp and rubber duct stuff for anything between the MAF and the throttle/final metal intake area, the bigger vacuum hoses that run off the intake system (brake booster, "suck valve" tied in with PCV set up, etc.), plus any small vacuum lines. When I triggered mine last week on the W12, I forgot to plug in the buried suck valve end that goes to the drivers side throttle rubber boot. I missed the big clamp retighten a few times on the A6 4.2 over the years when I pulled the air box for maintenance.

aTOMic

It's exactly those hard-to-diagnose, one-in-a-million problems that crop up which make me appreciate AW so very much! Thanks, bud!

Jake, you just cannot stay away from the D3 board, can you? (I'm glad, personally) I thought we lost you to those trouble-free D4s when you promoted yourself, mate!
To answer your question; there is one other engine code, 17981-Left engine solenoid-open circuit. There are other niggling codes but not in engine dep't (key unrecognized, steering angle sensor, etc).

Which points to what MP4...(did I ever learn your real name, if so I apologize; if not what is it?) is saying... Occam's Razor... check the simplest solution first. I did an oil change in a hurry recently and that's when the trouble started (give or take).

^^QFT, as they say.

One other odd fact: the MIL comes and goes. I wonder if I managed to get it through emissions while it was "off" if it'd pass. Another piece of info/red herring: all the readiness sensors show ready after two days except aux air pump. Hmmm.

Thanks guys!
-Tom

TSHong

I had 5 different codes when I got my car back from the shop. I can't remember them but 4 of them were lean codes. For me I knew it was going to be a vacuum leak and found a hose that was disconnected. It ran from a the left throttle body tube to a check valve and brake booster. I guess the check valve works because there were no issues with the brakes.

jakematic

I like to stay busy and help out around here if there's any value add I can provide.
Just be glad DoggyCop isn't busting your chops - heard he froze to a tree or something.


Not sure on 17891, but am in total agreement with MP4.2+6.0 and TSHong on vacuum.

TSHong

Not sure about the 17891 code either, even Ross Tech does not know that code.
Is there a Pcode for 17891?

MP4.2+6.0

text description sounds like the classic motor mount error for the hydraulic mounts. I often see codes for those when people post scans on older D3's. I used to get them on my old C5. If it is that, I would check the connector on the drivers side motor mount sometime when you have the belly pan up and can reach it more easily from below. After that, if I have the right code in mind, it is saying the mount has a problem. You can also run a self test of the mounts in VAG COM which causes the solenoid to click if they are functioning electrically. Separately, you can also look for the classic brown staining around them if they have cracked open and the oil has leaked out. Happened on my front torque mount, which is not solenoid controlled like the main mounts are. Fortunately I found it while still under CPO and the dealer repaired--a major pain on a W12 labor wise.

aTOMic

17981, as I said.

Perfunctory look this AM shows everything appears connected, but I would like to see where that airbox flap vacuum hose attaches to the engine.