Bryans12v

Ive been getting this code for the past month or so and it has me stumped.

17912 Intake Air System - Leak Detected/(Bentley Term. Bypass Air Detected)
92-00 Unknown Error Elaboration

If I could describe the running conditions:

Steady driving, car stumbles lightly throughout rpm range. At shift, the car stumbles heavy into second and third gear. So far, Ive replaced all my vac. lines (again) and checked the second stage of the TB to make sure it was closing properly. Ive also read in the Bentley manual that the Idle Air Control (IAC) Valve could be mechanically malfunctioning.
It says this here rotary slide could be sticking of just worn.
<img src="http://pictureposter.audiworld.com/21601/iac.jpg">

Basically, Im down to nothing, I cant figure out what the hell is throwing the code. I also read something in the manual that I would like some feedback on..

" If the malfunction "P1504 / 17912" is recognized, both power output stages ("+" and "-" output) are switched off. The Idle Air Control (IAC) valve -N71- has no power and opens the limp home cross section. "

Limp home cross section? Is my car in Limp Mode?

This all came about after I had done the intake work to my car. Here you can see what I mean by intake work..
<img src="http://pictureposter.audiworld.com/21601/collector_1.jpg">

<img src="http://pictureposter.audiworld.com/21601/intake_2.jpg">
Comming off the back of the collector.

<img src="http://pictureposter.audiworld.com/21601/inatke_3.jpg">
And up into the bottom of the airbox.

I have properly sealed up all cracks and holes. Now being that my car is a 12v and Im running the stock ECU , would this sort of induction cause my car to throw this code? Would it consider this force of air a leak or would it be something else?

I need some help here guys. I would never let anyone touch my car other than myself so bringing it to the shop is out of the question for now.

Any feedback is appreciated!

Thanks guys,

Bryan -

SlvrBullet Unloaded

the ram air spiked the voltage beyond the sampling rate and the mass air is FUBAR! try a new one.

Bryans12v

I wouldve gotten the ..

16487/P0103 - Mass or Volume Air Flow Circ High Input

followed by some lean running conditions , right? This was the only code it threw at me and its been consistent( cleared it, popped up again in a matter of seconds, then again and again). All of this was at idle so it wasnt really ramming iar through the MAF. It could be..

oz99

That code covers the MAF. If you've checked all the hoses and there are no leaks then you probably screwed up the MAF. They have been known to go faster with big turbo kits and I've heard with some people messing with intakes, like your intake. You could try taking out your MAF and cleaning. But it in a bag of isopropyl alcohol, and let it dry. Don't blow it off, try not to touch it and don't use other cleaners. If that doesn't work then you'll probably need to buy one (about $340 bucks) and take apart your intake. Good luck.

Audi2ptzero

your car will run rich not lean, which might give you that studder all the time. You will run lean when the maf is starting to die since the readings will be lower then normal.

Audiboy

in it's MAF sampling range at WOT. Only way to pass it is large psi forced induction.

Doesn't hurt to clean it, but I think the problem is more in a vacuum leak detected by a leak down test the OBD does to check for stored vacuum or vacuum path integrity. Other than that, I can't see any way for the ECU to check low vacuum - unless it is so severe it causes bucking and stumbling i.e. misfire and hesitation - then the sum of all sensors don't make sense so other codes will be thrown.

I'd check vacuum lines above the TB, and next to the MAF (Vacuum switches and sensor) Also the wiring connection.

Bryans12v

I have replaced all the vacuum lines over the plenum and TB.

Now, the car seems to run good, not as perfect as it did but good. Doenst stumble anymore.
The thing is, Im not sure if the car is still in the limp home cross section stated by Bentley. The MIL is still on due to the fact that I dont have my VAG Cable yet so the error is still reconized by the ECU even though I replaced the lines. It may not be intermittent but it is reconized..

This is what the Bentley says...

" If the malfunction "P1504 / 17912" is recognized, both power output stages ("+" and "-" output) are switched off. The Idle Air Control (IAC) valve -N71- has no power and opens the limp home cross section. "

So im guessing that even though I replaced all the lines, the error is still reconized(MIL still on) and Ive still got no power to the IAC untill the code is cleared from DTC memory . ?.? Right path?

Audiboy

(meaning no power to it) it will go to it's default setting of a small bypass hole enough to get the car idling - and not stalling. The IAC is the only source of air for idle when the throttle plates are closed. In older fuel injected cars, the idle can be set with a screw on the throttle body - or more commonly a bypass path with a cone shape screw.

Now, without knowing the logistics of how Motronics 7 works with this IAC, I am willing to bet the way the computer tells if the IAC is working is it will fine tune it and measure rpm and see if there is a good corelation. Since the IAC is a device driven by the ECU's output, it has to receive input from somewhere to see if the output device reacted to a change - and I think that will be the rpm (through the cam or crank position sensors.)

So the fact that Bentley asked to check other things - like maybe vacuum hoses and the secondary flap was because something was causing the expected idle rpm to be off from the computer settings. I've been running secondary flaps modified and got no codes from them - hmmm did I ever share that mod too? Sorry too many to list he he.

Here's a suggestion - check your IAC to see if it is stuck. Get a 9V battery and some wires - preferrably with aligator clips. Connect to the IAC and listen. Reverse connection and the motor should turn back up. That's all it is anyway - just a DC motor - or at least that's what it looks like plus the fact there's only two wires on it. Check the resistance of the 'motor' - It should probably have anything from maybe 5ohms to 10 ohms - as most wire coiled motors have that value. Anything lower is a shorted motor, much much higher is a open coil or bad brush - bad IAC

Another thing, see if you can tap into the two IAC wires while driving (maybe tape your DMM into the windshield) and just monitor the votage goes up and down as you drive around. That will at least tell you that there is voltage going into it, and the CEL is just on because it has not been reset.

Get a vacuum gauge - tap into the FPR and measure steady state idle and cruising vacuum. Should be steady around 21 mmHG (I can't remember the units). If erratic - vacuum leak somewhere.

BTW, this kind of thinking was how thought of a way to bypass the 12V EGR functionality - and I won - no codes and more acceleration - and a simple 1 minute tweak

Bryans12v

Why and how you bypassed the EGR. I hate being one to have the exhaust gas recirculation. I never understood why its on some and not on others. Please oh please share!

You can email me if neccesary.

Audiboy

then check your email btw, that's from my work email. Email that one back for faster response.