Rough idle (again)

[Graham1990]

I posted a bit about a rough idle on my 2005 mk5 gti the other day. The post won’t seem to load up for me to update it now so I’ll make a new one. Anyway I’ve just been out to pick the Mrs up when I got there I sat out the front for a bit just to see how the car was idling and it was awful. Feels juddery like it’s misfiring so I turned the car off went in to the in laws for 15 mins came out started car, drove home.  when I got home I sat in the car for a few mins and let it idle and it was perfect 🤔. I was thinking it may be the intake valves being covered in carbon but surely if it was the valves it would idle rough all the time? Not every now and again? I’m now thinking maybe the butterfly valve/plate in the throttle body may sometimes be getting stuck slightly open and allowing to much air through for idle. It drives perfect doesn’t stutter, hesitate at all. It only has the judder/misfire at idle. Any one got any ideas ??

[Graham1990]

Forgot to mention I have replaced:

Spark plugs
Coilpacks
Thermostat
Coolant
Oil and filter
Oil pick up pipe
Diverter valve
Cam follower
Air filter
Coolant temp sensor
In line thermostat
N205 camshaft adjustment valve.

I know some of them probably won’t solve the issue but they needed doing anyway. 👍

[Mitch H]

Check pcv
Try a throttle body reset
Pull injectors out and test them and clean valves at same time.
In that order

[Dan_FR]

Firstly - unplug the MAF with the engine running. If it stabilises then it points to an air leak. Secondly I would suspect the PCV valve as mentioned above which is a 5 minute job to check by simply blowing down the pipe

I've never known a TB reset solve anything on these cars, and jumping straight to injector pulling testing is a big and expensive step, plenty of other things to check first. A fault code scan (using something VAG specific - VCDS - as generic OBD2 code readers miss a lot of codes that don't trigger the EML) and a check of the Block 032 trims using VCDS would be useful too

[Graham1990]

Thanks lads, I have scanned the ecu and it has no codes. I haven’t bothered with pcv as I thought the symptom of that was more the engine going up and down the revs a few hundred or so rpm. I will try unplug the maf and see what happens and I will also check the pcv. I’ll report back and let you know what I find 👍

[pudding]

If only the idle is lumpy intermittently but all other loads and rpms are fine, it's either an air leak as already mentioned, or injector(s).   

An air leak at idle would normally show a larger than normal positive percentage in the long term trims (block 32).    Idle normally sits around 1.5%, if it's 5% or more, you probably have a slight leak.

If the trims are very low, I would put money on a lazy/partially clogged injector, given that you've replaced everything else.  Try giving it death on some quiet roads to wake the injectors up a bit.   Short journeys are the bain of these cars.

[pudding]

P.S. Where did you get the N205 (06F109257C) valve from?  I see they are £20 on ebay for a very obvious Chinese copy, and look to be well over £100+ for the official VW part!

[Graham1990]

@Pudding I got the n205 from vw i think it was £98 including vat I’ll check the receipt when I get home 👍

[Graham1990]

Yeah the n205 was £98.40 from vw. Same part number as you mentioned. Any suggestions on the easiest way to find an air leak? Cheers.

[Mitch H]

Yeah the n205 was £98.40 from vw. Same part number as you mentioned. Any suggestions on the easiest way to find an air leak? Cheers.

Smoke test

[pudding]

Yeah the n205 was £98.40 from vw. Same part number as you mentioned. Any suggestions on the easiest way to find an air leak? Cheers.

Thanks mate.  I physically checked mine yesterday, and also tracked it's adjustments with VCDS.  It's fine, so £100 saved 

Mine also has a lumpy idle intermittently.  Seems worse when it's cold.  My car is a bit like me, it prefers the warmth of summer!

[Graham1990]

Yeah the n205 was £98.40 from vw. Same part number as you mentioned. Any suggestions on the easiest way to find an air leak? Cheers.

Thanks mate.  I physically checked mine yesterday, and also tracked it's adjustments with VCDS.  It's fine, so £100 saved 

Mine also has a lumpy idle intermittently.  Seems worse when it's cold.  My car is a bit like me, it prefers the warmth of summer!

Haha it’s always nice when you don’t have to spend money on boring parts. I hate intermittent faults, it seems they are all I ever get. I have actually noticed another symptom that may be linked. Sometimes it will struggle to start. Not the battery that is fine and turns the engine over really well. If you keep the key twisted it keeps cranking and eventually fires into life. Sometimes if you twist the key and as it starts let go it will die, then you twist the key again and it fires up fine. Does this help anymore with the diagnosing? Thanks

[pudding]

You could try cleaning the MAF with some Isopropanol alcohol, or 'MAF cleaner'.   If not that, it's probably injectors or an air leak.   Idle is where you notice a dodgy injector the most.

[Graham1990]

You could try cleaning the MAF with some Isopropanol alcohol, or 'MAF cleaner'.   If not that, it's probably injectors or an air leak.   Idle is where you notice a dodgy injector the most.

Thanks mate, all I want to do is get the thing remapped! 😩 it was booked in for the 3rd of Feb but I had to cancel because of the code coming up which was the n205 in the end. I really want to sort the dodgy idle before I book it back in for the map. I’ll be checking the maf, pcv and have a visual check for leaks tomorrow. If all seems ok I’m going to get the engine smoke tested next Saturday. See if I can see any leaks. If not I’ll be replacing the injectors and cleaning the valves while I’m at it 🤑🤑

[Graham1990]

Firstly - unplug the MAF with the engine running. If it stabilises then it points to an air leak. Secondly I would suspect the PCV valve as mentioned above which is a 5 minute job to check by simply blowing down the pipe

I've never known a TB reset solve anything on these cars, and jumping straight to injector pulling testing is a big and expensive step, plenty of other things to check first. A fault code scan (using something VAG specific - VCDS - as generic OBD2 code readers miss a lot of codes that don't trigger the EML) and a check of the Block 032 trims using VCDS would be useful too

I had two mins spare earlier so I tried what you said with the maf. The engine was running I unplugged the maf and the car very nearly stalled and then it ran like normal. So I plugged the maf back in, started the car, tried it again and the car died immediately. Then I plugged the maf back in and the car wouldn’t start at all, tried for a while with no joy then tried again with the accelerator down a bit and it started and ran fine again. Any ideas ?? I will check the pcv tomorrow when I have a bit more time spare.