Sometimes High idle, revs jumping when shifting, rev hang, slow rpm drop

[crookedd]

Hi guys!

So i have had issues for maybe 5 years now. They are not too bothersome but would like to get them fixed if possible. So opening this thread and hoping to try and troubleshoot a bit with you guys. There are a few issues, im not sure if they are all related.

Manual MK5 GTI 2006

High idle: This only happens the car has been up to temperature for at least 10 minutes. It only happens sometimes, not very often. When coming to a stop and putting the car in neutral, the revs with go up slowly to maybe 1500 or 2000 rpm, stay there for 1 or 2 seconds and slowly drop again, sometimes staying at like 1200/1400, sometimes dropping to normal idle(680 ish?). When it hangs at 1200 and i give the engine a "bump back down" by tapping it with the clutch, sometimes makes it stay at normal idle, sometimes they rev back up to 1200/1300 again.

Rev jump when shifting. When shifting under high/full load and not near end of rpm range(lets say between 2K and 4K) When i let go of the gas and push the clutch in, the revs might quickyl jump up 200 to 400 rpm or so and then drop. This happens quickly, maybe in 0.5 seconds or so, but it feels like power gets cut just a bit later then me letting go of the gas/pressing in the clutch. This is anoying want to do a short mini pull not to the end of the revs and then just shifting normaly, make me have to wait like a second before i can let the clutch come up in the next gear.

Rev hang when shifting. This bit similar to the one above but just in genreal when driving normale shifting at 2 - 2.5k rpm. The revs hang takes a bit to go down. When engine is cold its super normal and drop back down quickly. When the engine is warm every shift is very slow. Since i have gotten used to it isnt to bad but its drives so much nicer when the car is cold. Also having the aircon running makes a slight but noticable difference, this rpm drop a bit quicker then when its not running.

Idle(when not having the issues above) is ever so slightly choppy. Feels like it misfires every 10 seconds, but just very slightly.

Car is at 172k km, bought it at 102k km in 2017. Cold air intake, DV+, 200 cells sportcat. The car was already tuned going off of the boost values, but i have no clue by who. How likely would it be that it is a bad tune?
Replaced PCV(06F 129 101 R) in 2021 without a difference. DV+ since around that time aswel. Did a smoke test at garage for vacuum leaks, nothing was found. Finally had a carbon clean done a few weeks ago, no improvement.(i can share before/after pictures if someone cares).

Not sure what my next step is to fix this? I have OBDeleven, anyhing i can log or something?
My gut says there must be a vacuum leak or some air coming in that is not accounted for by the MAF, but smoke test rules this out no? Maybe get another shop to have a look?

Things i might try:
Clean MAF? I can also try with a friends MAF.

Replace clutch position sensor/hall sensor(1K0927810D Clutch Position Sensor G476).
Been reading a few threads where people said this could help. I doubt its faulty since i use cruise control every day for 80% of my driving and i have never had it not work or cutout/stop. Woundt a faulty sensor cause CC to cut out sometimes?

Replace N80?

Let me know if you need more information. I welcome all suggestions and tips. Thanks so much!

[ZoliWorks]

I used to have rev hang in my car, 128k km at the time. When shifting, revs would slightly increase or stay where they were and the car would still pull after letting off the clutch (without giving it gas). Revs would also sometimes drop fast, other times drop very slowly.

In my case, it ended up being a worn out/clogged VVT system. I changed the chain, tensioner, the adjuster sprocket, the 3 plastic control rings and the regulator module itself. The sprocket is the most expensive of them all, costing about 300 euros at the time.

All parts were INA. No issues since.

[crookedd]

Thanks, i had the tensioner and chain "kit" done a few years ago because on startup you could hear the chain rattle. Not sure what exactly is in this kitbut im doubting its everything youre talkinga about. What exactly would the "adjuster sprocket" and "regulator module" be?

[ZoliWorks]

• 3 - camshaft timing chain - 06D109229B
• 4 - camshaft chain tensioner - 06F109217A
• 6 - camshaft adjuster sprocket - 06F109088J
• 7 - camshaft adjuster bolt - 06D109281D - single use, will strip head upon removal, requires VW Tool T40080 to install/remove
• 26 - camshaft adjuster regulator/controller - 06F109257C

The way this works: The adjuster, also known as the N205 opens/closes to direct oil flow through itself into the variable sprocket. Using oil pressure, this adjusts the rotation of the intake camshaft (IIRC). Overtime both can get clogged due to the gunk that deposits on them from the oil. This slows down their movement or sometimes seizes them completely. It's usually the variable sprocket that has issues, but I changed both just to be sure.

These generally have a lifetime of 100k km but can last over 150k depending on how you drive the car, what oil you use and how frequently you change it.

By lifetime I mean work properly in their factory parameters. You can still use them until they seize completely or until your car starts throwing a CEL. You'll just have a slower response, rev hang and maybe less power.

[ZoliWorks]

But yeah, I did all this cause my engine would hang or respond slowly. It also started occasionally throwing a fault, saying the engine isnt timed correctly.

The revs raising and dropping by themselves usually mean a vacuum leak. You could have some split hoses somewhere maybe. I dont even know where to start on those. The oil dipstick has a rubber seal that can go bad. The plastic camshaft cover can also split, altho unlikely. The seal between it and the engine head should be replaced too cause after 100k km it's basically cooked solid. The PCV system should be checked as well. You should always use an OE pcv, nothing aftermarket. They dont last at all. I've had one go bad not even 3 days after installing. The N80 could get changed too but not sure if it would help. It's a $10 part and can be changed with just 2 clamps so it's cheap and simple. MAF maybe? who knows, but those are expensive AF new. Intake flaps adjuster motor? Intake-to-head seal? Hell, even the oil fill cap seal can cause vacuum leaks! I havent had issues with the DV+ when I was k03 but I would try a regular rev G dv just in case.

Also the brake booster vacuum hose. This is a 3 way hose that runs between the intake, vacuum pump and another plastic pipe thingy above the gearbox. This is solid plastic and I've had it split before. It would cause the car to have a massive vacuum leak and basically run on 3 cylinders.

There's soo many things that can go wrong on these engines. And they are especially sensitive to any kind of vacuum leak.