Can bad rear main seal cause poor idle (lean mixture)?

[zaku]

So here is the deal:
I have '09 B8 with about 100K
Got the APR stage1 a while ago.
After the last oil change I had done at Audi shop it kept telling me to drain oil for a couple of weeks. I only knew that because I accessed the car settings through the MMI to see the oil level after the change.
I did not think much of it for couple of weeks thinking it is settling down and the shop knows what they are doing.
They also serviced the transmission at the time and resealed the vacuum pump (it was leaking oil), valve cover gasket, changed spark plugs and coils (misfire). Anyway on Saturday my check engine light went on and while I was sitting at the light It kept telling me to shut off the engine and check oil. When I did it told me to drain it. I assumed the level was getting higher so I called the shop and went straight there. After some back and forth they determined that the oil separator unit was shot and it caused the pressure from the turbo blow into the crank case. I left the car there to change the separator. They have just called me back today and told me that my rear crank seal is bad from all the pressure in the crank case and is sucking extra air causing lean mixture and rough idle. Frankly I don't believe them as the engine is not leaking any oil. From what they told me there is some "wet" on the bottom of the bell housing but that could be caused by the positive pressure from the turbo in the crank case when the separator went bad. Obviously that's a big job and they want a lot of money for it but they claim this is the only way to make the idle smooth again and get rid of the check engine light.
I would think this is a known issue/problem with these 2.0 TFSI but could not find anything on this forum or the web...

[B44]

First of all rough idle can be a lot of things. I blame you for being lazy and not checking oil level with a dipstick. Now first of all post what codes you have like error codes. Second clean out your maf sensor and replace the pcv yourself it's not a tough job takes 20 mins while you are at pcv check thhe sparkplug and replace if needed clear the codes. Then after this disconnect negative terminal from battery for 10 mins connect it back start the engine and see how it drives also take it up to any shop lift the car and inspect the joint between trans and engine should be wet if it's dry then above should solve it. While you are at all this make sure you check all your boost pipes from intercooler to throttle body and hoses going to turbo. Hope this helps. Also if the rear seal is leaking you will have a blot of oil underneath the car if car is parked overnight. Good luck.

[zaku]

Thanks for the advice. I'll definitely check that.
Unfortunately there is no dipstick to check the oil level in my car. The only way to check it is via the MMI screen That's why I waited. Also the shop that did it specializes in Audis so I assumed they knew what they were doing and wanted to give it a little time. I figured if the oil level is a little high it won't hurt it much. It was a little odd because I left my car there when I went on vacation. They were supposed to only do transmission service, vacuum pump, wheel alignment (I never checked it after putting in the coil overs) and oil change. They ended up resealing the top end and changing the spark plugs and coils in addition.
It wasn't too much money so I figured I let them make some extra dough. The nice thing was that I picked up "fresh" car after I returned from my trip. Or so I thought....
Anyway -they insist it's the rear crank seal. They even say if they spray brake cleaner into the bell housing the idle smoothens as the crank case sucks it in with the extra air... I don't believe them... am I wrong?

[gdawg'05a4]

Rear main seals have been known to go bad on B8 2.0Ts especially with higher mileage. My friend's shop has replaced the RMS on a few B8s with over 100k miles. It can cause a lean code as the seal fails and sucks in excessive air through the PCV system. I recall a few owners posting about their RMS leaking and replaced with an updated part.

[B44]

If it's the rms I would suggest going to a dealer I got my replaced at 105k at around 115k it started leaking again dealer replaced without any issue. These kinds sometimes dealer is cheaper than local shop. Good luck.

[lx4life]

Is there a DIY on replacing the rear main seal on this engine? Also for the OP it is concerning that after you told your shop to do one thing and they replaced things without your permission or knowing doesn't sound right, it seems like they did something wrong and try to "fix it".

[Fburg A4]

I had a leaking rms and it did cause a bad idle and eventually I got a lean mixture code along with the CEL being illuminated.

[Militant-Grunt]

So here is the deal:
I have '09 B8 with about 100K
Got the APR stage1 a while ago.
After the last oil change I had done at Audi shop it kept telling me to drain oil for a couple of weeks. I only knew that because I accessed the car settings through the MMI to see the oil level after the change.
I did not think much of it for couple of weeks thinking it is settling down and the shop knows what they are doing.
They also serviced the transmission at the time and resealed the vacuum pump (it was leaking oil), valve cover gasket, changed spark plugs and coils (misfire). Anyway on Saturday my check engine light went on and while I was sitting at the light It kept telling me to shut off the engine and check oil. When I did it told me to drain it. I assumed the level was getting higher so I called the shop and went straight there. After some back and forth they determined that the oil separator unit was shot and it caused the pressure from the turbo blow into the crank case. I left the car there to change the separator. They have just called me back today and told me that my rear crank seal is bad from all the pressure in the crank case and is sucking extra air causing lean mixture and rough idle. Frankly I don't believe them as the engine is not leaking any oil. From what they told me there is some "wet" on the bottom of the bell housing but that could be caused by the positive pressure from the turbo in the crank case when the separator went bad. Obviously that's a big job and they want a lot of money for it but they claim this is the only way to make the idle smooth again and get rid of the check engine light.
I would think this is a known issue/problem with these 2.0 TFSI but could not find anything on this forum or the web...

Yep extremely common, I did one about a month ago. The seal literally blows out.

[zaku]

OK update.
I went to see the car today and the engine is leaking oil from the bell housing /engine block joint.
They also sprayed some starting fluid under the flywheel while the engine was idling rough and the idle smoothed out immediately.
I had no idea..
anyway- having the RMS replaced-$1200

[DPD314]

That's a lot of money - I think I payed $400 tops. Isn't that seal a $50 part - the only problem is where its located takes a lot of labor? I might have had a different seal go.

-Noob here though

[gdawg'05a4]

That's a lot of money - I think I payed $400 tops. Isn't that seal a $50 part - the only problem is where its located takes a lot of labor? I might have had a different seal go.

-Noob here though

Labor is the bulk. Transmission has to be removed to get to the seal.

[zaku]

Yes a lot of dough. I'll try to shop around a bit.
The thing is I've just spent $1800 on the transmission service, oil leak fixes and spark plugs/coils (and APR update and oil change) couple of months ago
Yesterday I paid $300 for the oil separator replacement and diagnostics.
Now $1200....
It starts getting to me TBH....:-(

[zaku]

I've just heard from a friend that's a VW /Audi mechanic. He says that most of the time in case like this the problem is NOT the RMS. The engine sucks air through the seals all the time anyway.
The problem most of the time is the wrong PCV valve. They deal with it a lot when the lean mixture code pops up at idle.
Apparently there are dozens of different ones for different engine types.
They all look the same but vary in the restrictions of the vacuum getting from the intake manifold to the crank case. If the wrong PCV valve is used it makes it very hard to remove the oil filler cap with the engine idling.(too much vacuum gets through)
That's how you can tell.
He told me to first make sure I got the correct oil separator unit when it was replaced.
I have no idea how to tell if it's correct other than trying to remove the oil filler cap while the engine is running and see how difficult it is.
any ideas?