So I'm 95% positive that I have a vac. leak. My car can barely idle, and it often sputters and wants to die when it is idling correct. My vac guage is now reading 12 in/hg at idle, and then goes to the normal 22 in/hg when I get up to speed. CEL just came on today, and the car is in limp, only boosting 1psi with a GIAC chip. MAF is fine, just cleaned it last week, car ran great. New plugs and coils put in two weeks ago. I pulled the N75, and there's oil dripping out of it when I removed it. I'm going to pull out all the injectors and take a peek as soon as it stops raining out, but my money is on vac leak....

where should I look for the most problematic vacuum hoses? Any diagrams to help me?
thanks

 

You have a CEL. It's probably smarter to get the fault code(s) from the ECU before getting your hands dirty.

 

Rubber vac line cost less than $0.50/ft, so buy 10ft and replace it ALL. The stock (Audi) braided vac lines dry rot too quickly and always start to leak.

 

I already did.

bank 1/1 bank 1/2 running lean

 

fuzzduster-where should I look for the most problematic vacuum hoses?

Id start with the lines running off the n75, the main one that gave me trouble was the line running to the wastegate...

 

All of them!

I, too, recommend reading the DTCs to see what exactly the MIL is on for before chasing your tail, but here goes:

Most common is the breather hose setup. There is a "T" at the back of the valve cover that gets oiled up and collapses or splits. Follow it down and there is a plastic pipe (or metal if you have a late AWM) hose that attaches to a formed rubber hose that also collects oil and collapses or splits. I believe there is a check valve in one of those hoses that can also cause an interior vacuum leak. Follow the "T" the other way and you'll find a series of rubber elbows and connectors heading towards the airbox that can also cause issues.

Check the oil dipstick tube for cracks. Pull up on the dipstick. If the tube comes with it, replace the tube.

Additionally, there are about 16,000 feet of 1/4" vacuum lines that become dry and are only held together by the exterior webbing. Check all of them. Most common is the line to the FPR. It's short and towards the rear of the head. Additionally, there is a long line that runs from the DV to the intake manifold across the front of the engine. It tethers to the timing belt cover and often can collapse or chafe through.

Hope this helps.

 

i also suggest checking this one out as it would easily explain your lean condition

 

when at idle there isnt as much vac suction from the engine so a small leak would make a difference here. when you get up to speed theres more suction power, enough to mask a small leak. my vac is around -25 idle -27 @3200 rpm. you probably have a (few) decent size leak(s)

 

Good advice there. There's also the small lines at the front and back of the intake manifold, which are very easy to replace. And it's not 1/4", I know it's a much smaller I.D. than that. Just get about 8-10 feet and you'll have plenty.

 

update-

so today I took the codes off the car after double checking all the common problems and took it out for a spin. Its running strong, and sounds like its boosting 16 or 17 psi (like it should be) but its only boosting 5, and drops to 3 around the 4.5 - 6k rpms range. Vacuum was still being weird. So I decided to get underneath the car to be able to get a better look at some of the hoses that drop under the engine.

I found that the thick hose running from the turbo, down, underneath the engine block (also connected to the DV valve), and to the SMIC on the other side, had the clamps off! The hose ends slip onto a metal tube that connects them under the engine, and the tube was dripping oil, and the hoses were almost all the way off. So I slid them back on and clamped them tight. So I'll see if the car will balance out the running rich problem tomorrow, and HOPEFULLY run like its supposed to.
Oh and I took off the fuel rail to look at the injectors, and the last injector towards the drivers seat, has a broken head. It has two long cracks running though it, and it can swivel around. When I pulled it out of its seat in the manifold, all this oil/gas bubbled out and started hissing. So I need to replace that too.