2009 MK5 GTI TSi Vacuum leak? Where?


New member
Campbell, CA
2009 VW MK5 GTI TSi

After registering for the first time, there is a problem with my 09 GTI TSi, so I post it.

2009 MK5 GTI TSi 127,XXXmiles & 6MT 5 doors.

Around April 2020, due to air intake problem:

+ April, 2020:
Replaced: Intake Manifold (3 times) + Cleaned the carbon build up + Fuel Injection System + Throttle Body + Spark Plugs including ignition coils.

I have a problem since a month ago, it's a long story.

+Idle hunting:

I checked that the RPM went down late when the car stopped, and after parking,
I stepped on the accelerator and it went down like an RPM hunting (No CEL).
The following day, the same symptoms were repeated when going to work, and the CEL was turned on.

1. Generic OBD2 reader: P0100 & P0507 -> Replaced new OEM MAF sensor then, cleared codes by myself.
2. After starting, RPM is unstable and the above symptoms appeared and CEL was back on: P0100 & P0507 & P0171.
3. Went to VW Speciality shop:
The owner replaced the Mass Air Flow sensor first (Throttle Body Side), and the MAF sensor was replaced.
And the problem is still existed -> CEL P0100 was ON.
Because it was a strange same symptom above, so the MAF sensor connector and wires were replaced but the P0100 kept turning on & PCV repaired (Not replaced whole new one).
4. If cleared P0100 with VCDS/VAC-COM, causing RPM to become unstable and stalled.
3 weeks ago, the owner couldn't find what the problem was,
So I took over the car because there was no problem operation with the CEL going around with the lights on.
The owner said there could be a problem with the PCM (He was not sure), which he couldn't solve & he said that just drive it.
5. I checked and erased CEL several times few days after took over.
The engine didn't turn off (if CEL deleted), so far and the car shook a little bit and the CEL turned on again after re-starting.
I can drive even if I remove the CEL now, but the car is a little shaky, and when the CEL is lit, RPM Hunting is created likely above, but nothing is rattling.
6. Since last week, the idle hunting has gotten worse (CEL), so visited another VW shop urgently.
They replaced both the PCV valve and the ignition coil + Spark Plugs (They told me that it's black color) with a new one, and after the test drive,
The above CEL came out again, first removing the PCV valve breather hose, then blocking the air intake port (pictured).
According to them, the Diverter valve is OK.

And then everything goes back to normal (no CEL).
They asked to get an oil catch can quickly.

This is California, so if I use the oil catch can, there is a problem with smoke test.

My question is:
Connecting the PCV valve breather hose to the air inlet:

1. Misfires.
2. Vacuum leak occurred.

If disconnect the PCV valve breather hose to the air inlet, all back to a normal.
It's drivable.

Here are some CEL Codes I noticed:

4 weeks ago:
P0100 & P0507 & P0171.

P0606 & 0101 & 0507 & 2279 & 0171.
Cleared and P0101 & 2279 again.
Cleared and P0101 & 0507 again.

Cleared and P0101 again.
Cleared and P2279 & 0101 & P0171 & 0507 again.

Cleared and P0101 & P0171 & P0507 again.

I understand that has to be rescanned on it however just wanted to get some tips.
Cause I spent over $4K since 2020 @ another 2 of VW shops.
I don't know what to do.

Be safe & healthy.


Joel J Benedict Lee


  • IMG_5438.JPG
    61.7 KB · Views: 8


2007 MKV GTI
Have you looked at the oil dipstick seal/o-ring? Obviously, with the dipstick o-ring able to trigger P0171 and P0507...any leak in the crankcase can do the same. Given P0100 is included in the may be a leak in the air inlet. Which can be anything between the MAF and the air inlets of the head. A thorough smoke test session may be required to detect any leaks. Has the PCV tubing themselves been checked for leaks? Or was only the PCV replaced? Does it run OK when the PCV tube is connected but the MAF wiring is disconnected? If so...and it has a good and proper MAF, then it has a leak or leaks. Also, it could be in the brake booster tubing.


New member
Campbell, CA
2009 VW MK5 GTI TSi
Dear Roh Echt

Thank you much for feedback.
The dipstick, I checked however not found it anything so far.
PCV Tubing did not check so I will check, PCV ONLY replaced I believed. However I found it back of PCV Breather Hose looks brand new one.
MAF sensor disconnect running will check too.

So far it's still running good w disconnected PCV hose as pic, and now I found it some tons of oil are dripping to the ground.
I wanted to call another VW Specialist soon.

Thank you again Roh Echt, will check it then, update.


New member
Campbell, CA
2009 VW MK5 GTI TSi
Dear Roh Echt.

Diagnosed & so far, rear main seal is broken they said. According to VW Specialist, this GTI with DSG auto is always has an RMS issues. But it happens with 6MT too.
Only replace the upgraded the main seal cost is approx. $2K.