Hey Guys,
The car ran perfect before I decided to change out the Aux water pump on my 01 2.7t A6. I beleive I have checked over everything and cant find anything I forgot to put back. The car now runs terrible and is throwing a P0300 code. Any help would be great!!!

Its a random multiple miss-fire fault code. It probably has nothing to do with the aux pump you just changed. Un-less you didn't torque down the intake manifold correctly you probably have a bad power output stage (ignition control module) or bad spark plugs. I would also double check to see if you pinched any wires going to the ignition coils, or if you didn't plug them all the way in.

Thats the thing, I didnt touch any of the ignition components and thought it would be awfully weird for an ignition component to just happen to go out right at that moment.

S*** happens. I would double check you didn't pinch the intake manifold gasket or forgot to plug a major hose in. If it all checks out, eventually you'll get a dead miss fire fault code on one cylinder and it should help you diagnose it for the bad ignition part. Most likely a bad ICM.

Yea no doubt S*** happens, it just absolutely amazes me that I can pull it in the garage running 100% except for a little collant leak and button everything up go t pull it out and now it runs terrible... I had to of missed something however you may be right. Is there any way of testing those ICM's?

You can't really test the ICM with available tools. You would need a pin out box with an LED lead that you would install on the wiring harness from the ECM.
However keep an eye on the fault codes, if it throws a dead miss-fire on like cylinder two perhaps, then you can swap the two ICM's from bank to bank and see if the miss-fire moved to a different cylinder. Both ICM's are sitting on the air box on a 2.7T. They should have a connector on both sides.

Could this thing have anything to do with the problem? I did some more looking around and noticed this was cracked, when I removed it the nipple fully broke off.....

local://upfiles/47422/BD36AA4A000D4262874A0BD74711DFEB.jpg

Yes it will have something to do with your problem because it is now dragging air into the system. bypass this if you can or replace/repair the item.

Yep, thats the culprit

Im still kinda conserned...... I didnt think that small of a vacuum leak would cause that much havoc. Does anyone know the function of that little vacuum fitting?

Its a vaccum check valve, it would be no small vaccum leak if that fitting was broken off though. The engine management ona 2.7T is extremely sensitive to leaks.
I wouldn't by pass it if i were you, its about a $40 part at the dealer, they are usually in stock.

sorry should have elaborated a little more on my reply, what i meant by by pass was for test purposes only, not to make the repair permanent, the valve does need replacing regardless. and yes a very small leak will cause all sorts of problems and i should know i do this for a living. regards Vinny, ps let us know how you get on, i am confident of the outcome.:D

Alright, I picked up that vacuum check valve today. Car started fine however the CEL still came on. It has a rough idle but thats just about it. The car drives perfectly fine and normal and as soon as I start moving the CEL goes out. If I let the car idle for more then minute the CEL goes back on however the rough idle never goes away. Any thoughts?

You probably still have a miss-fire, either you still have a small vaccum leak or the spark plugs are fouled up. Mine has a slight random miss-fire in my S4 at idle because my plugs are fouled up. But mine doesn't shake, so i would say its still a vaccum related problem.

I would have to agree. I just pulled the plugs and they look fine. Back to finding this damn vacuum leak!!!

Ok, I give up. I spent all day Saturday and now all tonight trying to figure out what this things problem is. I cant pin point it to save my life. I keep getting the same P0300 code even after driving it for a few miles. It drives fine but still idles terrible. I can hear a high pitched hissing telling me theres a vacuum leak but I cant find it without the proper tools. I guess ill be heading to a place I haven't been in 10 years... The local auto mech. I've rebuilt entire engines in my day and can tackle just about anything but this one has me stumped. Sorry for venting but this has me pissed!!![sm=headbang.gif]

Well before you go taking off to the mechanic i have one other place you can check. You have to take off the turbo Y pipe to get to it, there is a little white vaccum T fitting that commonly breaks off that i usually find when i smoke test the intake. You can try and take apart the motor to see if you can find it, or you can take it to the mechanic and have him smoke test it to find the leak.

Interesting. Its not the bigger one I just replaced is it? I can't recall seeing any white T fittings but I can certainly give that a look. Theres a whole swarm of large vacuum lines on the rear side of the engine that are not very easy to get to, that not where your talking about is it? Any specific location????

I took the liberty of taking a quick pic.:)

local://upfiles/47422/B490189354424FB69B49A3F0CE9CA211.jpg

Its wayyyyyy deep behind the motor, and it isn't that big.

A mechnic at one of my classes taught me a trick I've used with success on my Ford pickup, but I'd let let otherfolks here verify that this won't damage a turbo charged / high compression engine before you give it a whirl.

You can pick up a small propane torch from most any hardware store or even walmart then turn it on slightly and follow your vacuum hoses. The idea is that when you wave it over the leak it will suck in the propane and dump it into the cylinders. This gas will richen the fuel/air mixture and make the car idle faster.

So you basically are just waving the propane bottle around until you hear the idle go slightly quicker and you know you've found your vacuum leak.

However, I only know this works on a carburated,low compression engine. Your 2.7T has an electronically controlled idle which may negate this anywayandI wouldn't want to recommend anything that has any chance of damaging your car in anyway.

hello again, still got problems at tickover then. the smoke testand thegas test is perfectly safe, and yes even with electronic tickovers etc the engine speed will definately change so that you can pinpoint to a certain area where the leak is.your light that stays on when ticking over and then goes out when running above tickover sounds like an air leak. you will definately have disturbed something else as you have prooved by replacing the vacuum valve.that is why the light goes out after tickover because it is running ok. make sure the pipes you have fitted have been replaced in the correct order because if you havent then where itthere shoulda vacuum and it is not a vacuum the valve is not doing its job and the engine managment side of the system will pick this up and register this has a fault.but you must now check every vacuum pipe. by the way i have just looked in my auto data book and code 0300 lists the faults has follows. misfire detected, probable causes, spark plugs,ht leads,ignition coil(coils), wiring, low compression.be sure before you go crazy with the vacuum side of things that the electrical side of things are ok. looking at plugs and leads and thinking they look ok is not good enough. if you have not got proper equipment to check the items then change them or have somebody check them for you with diagnostic equipment.this can save loads of time and money. with over 30 years in the motor trade i have found on numerous occassions that a car has run ok when it came in to have a simple job done like yourself then it runs crap or wont start, whatever the out come it tells you one thing it is definately something that you have done or in this case disturbed, you only have to move slightly a faulty plug lead or a faulty bit of wiring and bingo you have a fault which is difficult to find, but you know it wasn't there before so backtrack and be 200% sure of everthing, hope i havn't bored you but i hope it helps, ps after 30 years i still get problems like yours and its a pain the arse. good luck vinny

man i have the same exact issue,and my repair tech told me he fixed a hose that had a blockage in the vacum lines, now im praying this to is my problem, where is this part located if you pleae?:D

I have dropped my car off at a mech to do a smoke test on the vacuum system. I havent given up on finding the problem I just have ran out of time. Im driving from the Philly area to NYC on Thursday evening and need the car 100%... Ill let you guys know the out come!

Well, what happened

vinney -- are you someone's cousin??? :D:D

Just a sugestion - it is hard to read a post with run-on together sentences. Please make it easier for us to read!