I seem to be having vacuum issues on my 2003 Audi A4 1.8T Tiptronic(AMB motor). To get to the chase I’ll state what I think is wrong and the symptoms/testing I’ve done; then I’ll list everything else I’ve done. It’s important to note that this is ***NOT*** a vacuum leak (as in hoses or intake/TB gaskets etc etc). I am also not having any misses or anything of the sort. I am on a stock tune, no chip. The car otherwise runs great and pulls hard. I've been working on turbo cars since I was 17 (1996) and am very familiar around cars.

My vacuum is the following:
In park: 19-20in/hg
In park with AC: 15-16 in/hg
In Drive: 15-16 in/hg
In drive with AC: 11-13in/hg (sometimes 14).

I also notice that my fuel economy at a stop seems to be pretty crappy. Highway driving will net about 25-32mpg, depending on how heavy my foot is that day. The car still has power and runs great, but I notice issues at idle, no one else notices anything wrong. I love this car but this vacuum at idle issue is just driving me up the wall… especially with gas prices these days… city driving does not have ideal fuel economy, but not absolutely horrible (20mpg on average.. 24mpg if I grandma it around).

I do not have any issues with boost. It comes on good and strong. No boost leaks.

I’ve done a compression test a few times without adding oil and once with adding oil, results:

Without Oil (with oil in parenthesis):
Cylinder 1: 170-175 (210)
Cylinder 2: 145-150 (210)
Cylinder 3: 175-180 (210)
Cylinder 4: 175-180 (210-240, not sure why this one got up so high).

I do not have a leakdown tool, but I felt the compression tests gave decent indication of what may be wrong.

In addition to this I have noticed bubbling /overflow in my coolant reservoir, but only with the cap off and not very consistently. I would say I've seen it maybe 5-10% of the time out of all the times I've monitored it. I do not have any loss in coolant, but I did notice some white smoke after changing my fuel filter. It was the only time I’ve seen/smelled it. I do sometimes, as of late, have misfires at cold start up. This seems to have really only started after doing the timing belt and CCT. I have no codes and everything was torqued to spec. Cam and crank both line up perfectly.

So I believe I have a combination of a headgasket issue and bad rings on cylinder #2. I have not pulled the head yet, and while it’s possible I may have a valve issue or cracks, I do not think it’s likely. On the dry test compression would drop off slowly after cranking was stopped, on the wet test the compression would hold fairly solid.

Does this seem like a likely scenario?

Now some things I’ve already done (listing because I don’t want to hear “Search the forum” or that I have a vacuum leak. I absolutely do not have a vacuum leak… so take it somewhere else). This list is not necessarily in the order that I did it:

Replaced the MAF
Replaced MAF wiring and connector
Cleaned MAF
Replaced Coils
Replaced intake manifold gasket
Replaced all exhaust gaskets
Replaced VC gasket
Replaced TB gasket
Cleaned Throttle Body
Performed TB alignment via VAG
Replaced Oring on IAT
Cleaned IAT
Replaced both Coolant Sensors (back of head.. used green top, and at the Radiator)
Replaced Turbo inlet pipe (forge)
Disconnected N75 from Turbo and capped off(still plugged in) for XS HPBC (set to 8psi)
Replaced stock intercooler and hoses with FMIC
Replaced Turbo (running K04 now)
Replaced clogged cat with Test Pipe
Installed EGR block off plate. Also replaced O-ring twice just in case.
Performed Vacuum/check valve simplification
Serviced Vacuum Pump (remember I have a Tiptronic… aka sucktronic)
Replaced Crankcase breather elbow for 034, ring, etc… (currently vented to atmosphere until Catch can comes in. Pancake valve is out of the picture)
Completely disconnected **ALL** vacuum sources and capped/clamped outlets on intake manifold
Replaced Serpentine belt
Replaced Timing belt, tensioner, roller, Cam seals, and Cam Chain tensioner. Checked timing and it is correct when rotating the engine, Still have 16 rollers between the cams.
Replaced water pump
Replaced Thermostat
Replaced spark plugs (NGK BK7RE) several times, tried .032, .030 and .028 gap
Read spark plugs, ground strap and porcelain base do not indicate lean or rich. They also are not wet from coolant or covered in oil. I’ve read the plugs when they were semi new (2 weeks old) and when they’ve been run for 3-4 months.
Replaced fuel Filter
Cleaned injectors
Performed Trans adaptation via VAG
Check countless blocks throughout a significant amount of time.
Block 032 averages about -3.4% and -1%-2% on the respective fields.
MAF reads about 3g/s in park. Goes up to 4-5g/s in drive and about 6g/s (up to 6.8-7 sometimes) when in Drive and the AC is on.
Changed oil numerous times (not necessarily for this but thought I’d add it. Using Castrol Syntec 5-30w I believe… might be 40w).
Checked voltages and resistance across MAF, Coils, Injectors, Alternator, a/c (probably anything electronic I could find in the engine bay.) And everything is within specs
Tested all grounds (they were ok)
Performed pressure test from TIP while spraying soapy water. No boost leaks.
With the car running, sprayed Brake Cleaner, Carb Cleaner, Propane… just about anything you can think of… with no change in idle or vacuum. Checked hoses, intake manifold, injector seats…. Everywhere.. hell I even tried it at the brake booster, both in the battery tray and from inside the car at the firewall.
Replaced Dipstick and tube.
I’ve tried several attempts at seafoam through the intake and fuel tank. Tried it in the crankcase and changed the oil as a last attempt at seafoam.
Replaced oil pick up tube (no sludge issues.. just did it as a precaution)
Tested Fuel Pressure at rail, tests good.
Tested oil pressure, tests good.
Tried Idle adaptation. No change in vacuum no matter where I set the idle.
(That’s just off the top of my head. The list goes on, if you want to know something more specific then just ask me. I’ve probably done it and can tell you the results).

So with that said, I have a Polydrive tool on the way. The head gasket and bolts will need to be changed regardless, but does my primary diagnosis of piston rings and secondary of head gasket sound accurate? If the rings don’t have a good seal then I piston wouldn’t be able to draw as much vacuum as it moves up and down in the bores.

What get’s me is that while cylinder #2 is lower than the others, it doesn’t seem like it is low enough to create a 9-10in/hg drop in vacuum when going from Park with the ac off to going into drive with the a/c on.
As I drive and the car get’s hotter (temp gauge is where it should be.. just mean as I drive the car for more than 10 minutes) the vacuum, in Drive with the AC on, will go from 10 to 13-14in/hg. I believe this is because the seals expand a bit more and create a slightly better seal.

I also know that an automatic will put more load on the engine since it is always engaged, but going from 19-20in/hg in park, to 15-16in/hg in drive (AC off) seems drastic. Another 5-6in/hg drop just by turning the AC on seems ridiculous.
Please tell me, what are your thoughts on this? Again I am getting no codes, timing is not being pulled. If you want specific logs then please let me know and I’ll happily provide them. Most importantly… this is not a vacuum leak, at least not in the way that everyone is so quick to jump to (remember I completely blocked off all vacuum locations and had the same vacuum pull).
Again, any genuine thoughts on what the issue may be in relation to everything I’ve outlined above would be appreciated.

Thank you very much.. also please don’t be annoyed but I will be cross posting this on other audi forums as well to try to pool together as many great minds as I can.

Thank you,

-Rich