1.8T : Vacuum leak or something else that I've caused

[FNK]

Hello everyone,
I am in dire need of help. It’s like regular help, only it’s dire.

This weekend, I replaced my air filter, removed my throttle body and cleaned it, same for the Air intake temperature sensor that is next to the TB. Also, I my hand went behind the engine trying to touch the “rear coolant flange” as I have a nice leak.

When starting the engine, the idle was very rough, so I did a throttle body adjustment (TBA) using VagCom. The lower/upper limit code was no more, but the rough idle remain.

Diagnostic;

1. I’ve bought a starter fluid for small motor, so spraying it all around would increase the Idle, thus identifying the vacuum leak (if any). Nothing, no increase in idle or sound.
2. MAF, I’ve unplugged the MAF nothing changed in the idle, then replugged it nothing again. I’ve logged the MAF value and I have a peak of 139 g/s at 6200 RPM (about 163 hp). This is the normal value.
3. I’ve bought hose clamps to test every check valves. (Not done yet).

Other symptoms;

•Brake booster not working, happened 2 times at start up within a week, otherwise it work fine.
•I can no longer hear or feel the turbo.
•I can no longer hear the Diverter Valve (DV/Bypass).

I need your help!

Edit : Audi B6 2003 1.8T AMB Quatro

[MacFady]

Just to clarify, does the car feel rough at idle or you have a wandering RPM at idle? Does the rough idle change at all when shifted into neutral (not sure what tranny you have). Do you have a boost gauge and what does it read for vacuum, boost etc.? What happens if you have the car idling and try to remove the oil cap from the valve cover ie: comes right off or takes a lot of force to remove with subsequent change in idle.

[FNK]

To answer your questions

Just to clarify, does the car feel rough at idle or you have a wandering RPM at idle?

Rough idle and the needle bounce like it will stall, then the throttle body open, the RPM jump, TB close, then RPM dip, etc.

Does the rough idle change at all when shifted into neutral?

Car is manual. Same idle.

Do you have a boost gauge and what does it read for vacuum, boost etc.?

I do not have a boost gauge.
Can I read thoses values using VagCom?

What happens if you have the car idling and try to remove the oil cap from the valve cover ie: comes right off or takes a lot of force to remove with subsequent change in idle.

I will try this in 2 hours, after work!

[old guy]

How high does the RPM take to jump up and how high does it go? Is it repetitive as a steady climb and then drop off, steady climb and drop off at regular intervals or is it just really rough like it's struggling to run?

You also mentioned a loss of brake boost. Have you checked your SJP?

[FNK]

Idle is struggling to stay steady.
Cold it's struggeling + massive misfires
Hot, it's rough because of all the misfires.

SJP? (Sara Jessica Parker?)

[old guy]

Suction Jet Pump. A common failure point. When it splits open you get rough idle, reduced braking power and loss of boost.

[bwizard]

The vacuum line came off my wife's 1.8t from the n249 solenoid. No turbo sound no boost, ran rough. Check that one . I put it back on all good now.

Sent from my HTC6535LVW using Audizine mobile app

[FNK]

I have more answers to the questions;

What happens if you have the car idling and try to remove the oil cap from the valve cover ie: comes right off or takes a lot of force to remove with subsequent change in idle.

There is no suction when removing the Oil dip stick or the oil cap. When removing the oil cap, the is even some ventilation out of it.

It was cold this morning and at idle I had NO brake assist. Brakes where only working when the car was moving, engine load corrected the issue until I came back to idle. When the engine is hot, the idle give me brake assist.

A. Can the PCV (Pressure Control Valve) make this issue?
B. Can the Suction jet Pump and the Pressure control valve be cleaned with some light oil (WD-40, supposing they are dirty)?

[old guy]

You never commented on whether or not you looked at your SJP. If it pulls apart like this it is defective.

[EuroxS4]

judging by the symptoms I would be leaning to a failed pcv or breather hoses.But it sounds like the car has a very large vacuum leak.

[Furly]

You never commented on whether or not you looked at your SJP. If it pulls apart like this it is defective.

Listen to this man right here. He is a wizard with these cars and this might just be your problem. Takes no more than a few seconds to check this.

[FNK]

Yes I've taken a look at it and it was separated in two.
I've glued it back together with no changes...

A friend got me two used, but functionnal, JSP.
I will swap them tomorrow.

A question :
When I remove the oil cap, should I have a hard time removing it while the car is working (strong vacuum)? I have no restrictions.

[Luxus Panzer]

Suction Jet Pump. A common failure point. When it splits open you get rough idle, reduced braking power and loss of boost.

What is the standard test for the SJP to detect cracks/leaks.

Standard boost leak test will find it?

Does a leak blow or suck at idle? if it is a blow, I could just use my hand or smoke. If it is a suck, can I use a unlit propane torch and listen for RPMs to go up?

[old guy]

What is the standard test for the SJP to detect cracks/leaks.

Standard boost leak test will find it?

Does a leak blow or suck at idle? if it is a blow, I could just use my hand or smoke. If it is a suck, can I use a unlit propane torch and listen for RPMs to go up?

Boost leak test will definately show if the SJP has separated. If the parts are still aligned you may not know it at idle since it will be under vacuum and the vacuum can hold the two parts together. However as soon as you get into boost they will separate and become a massive boost leak.

[MacFady]

What happens if you have the car idling and try to remove the oil cap from the valve cover ie: comes right off or takes a lot of force to remove with subsequent change in idle.

A question :
When I remove the oil cap, should I have a hard time removing it while the car is working (strong vacuum)? I have no restrictions.

A problem with the PCV or the PRV can cause either strong sustained crankcase suction (hard to remove cap) or alternatively a lot of positive pressure. If you pop off the cap and put your hand or a recipe/index car etc. over the hole you should feel subtle/mild alteration between blowing out and sucking in (insert joke here), but not a noticeable amount of either one or the other.

[FNK]

Alright I've found the culprit!

I've built a pressure tester, then;
1. Pressurized the air intake. No leak
2. Pressurized the intake manifold. Leak audible and easily identifiable using soapy water!

Yes I did separate the SJP, but after glueing it was fine again. I’ve put a new one in just in case.
The real culprit was the Check valve [06A133528A] exiting the valve cover and leading to the piloted check valve for crank case ventilation. Hot gases flow true it and it disintegrated when I’ve touched it, it was already separated in two causing the first leak.
I’ve replaced it temporarily, idle is better and the brakes are fine, but the rough idle and misfire are still there at idle.
I suspect a small plastic part of the valve got to the piloted check valve and prevent proper working function. From a description I’ve found, if that valve got damaged, it act as a vacuum leak, even if internal, causing the symptoms. We'll solve this!

I will be able to verify it shortly.
What a PITA that vacuum system!

[FNK]

I am simply posting as a closure for future references,

3 vacuum leak sources;

1. Half moon cam tensioner
I had an hidden leak under the Cam chain tensioner. The half moon was dried and shrunk quite a bit on the oil side (inside).
It took a good 3hrs to remove the valve cover gasket, then loosen the cam tensioner. No need to remove the cams or to use a "special tool". I welded one and did not even botheredd using it.

2. Check valve
There was a check valve pumping the air from the valve cover to the intake. It was snapped in two and pumping fresh air. Quick solve.

3. Throttle body plate misaligned
This one is my fault, as I did loosen the bolts on it to clean the TB, but failed to center it correctly. So the TB plate was off by 1/32, but it was enough to prevent the plate from closing completely at idle. Therefor, it was causing a massive vac leak! With the bolts looses, simply push against it to put it in closed mode, then torq the bolts. Done deal.

I've learned quite a lot about the 1.8T in the process and my vacuum system is in top notch shape now!