Carbon on valves?

[Chickensaur]

I made a post a while ago about my GTI having 2 knock sensor codes. Lately that has developed into a full-on misfire, but only under hard acceleration (so far just in first above ~5k). I replaced the coils and plugs, which helped a lot but it'll still misfire, just doesn't lose power as quickly as before. Anyway after some research I learned a really common issue that causes this is carbon buildup on the valves, which sounds like it could be it. The car has almost 100k miles, I think it's like 300 away. The misfire is always in cyl 2, wondering if theres anything else to look at.

[mjmallia]

Carbon build on the valves is very common with direct injection.

Clogged injectors is also another

[breeze]

I thought injector as well. If you are close to R-Tech give them a buzz. They do a reasonably priced inlet clean and injector service, and will have new injectors if you need them.

You say you replaced coils and plugs but you may want to swap the coils at least to see if your misfire moves. Very unlikely but zero cost. You could also try a couple of tanks with injector cleaner in it. I’ve used Liqui Moly 5153 before. No harm in trying.

[mjmallia]

At those miles I would say you def need a carbon clean for sure if it has never been done.

[SANDEGTI]

I thought injector as well. If you are close to R-Tech give them a buzz. They do a reasonably priced inlet clean and injector service, and will have new injectors if you need them.

You say you replaced coils and plugs but you may want to swap the coils at least to see if your misfire moves. Very unlikely but zero cost. You could also try a couple of tanks with injector cleaner in it. I’ve used Liqui Moly 5153 before. No harm in trying.

Do you put liqui molly in just after you filled the tank or does it not matter and can put it in any time? I ordered some last night, have a rough idle and with 140k I think they are the original injectors. Hoping this improves it somewhat. 

[breeze]

I used it a bit randomly to be honest. First was a full bottle and around half a tank. I probably used 3 cans/bottles over a 6m period.

First bottle definitely smoothed things out in a way that was quite obvious. Next two less so but I don’t see why they would not have improved things; just to a lesser extent.

High octane fuel, an Italian tune up and some injector cleaner. Like I said, not expensive.

[SANDEGTI]

Thank you, just got an update to say it's arriving tomorrow and now I can't wait to put it in the tank. 

I'll see what happens after the first bottle, I've only ever used premium fuel and it gets a good Italian tune up every day. Apparently Liqui Molly continues cleaning for 1.2k miles which is interesting. Heard a lot of good stuff about it.

[pudding]

I stopped using the Liquimoly as I found myself putting a can in with every refill to keep the idle smooth.  It was becoming an addiction.....I could see myself being a 3 cans a day man 

When I stopped using it, the idle got rough as a badgers arse for about a month, but then smoothed out again.  I think that cleaner removes a 'cushion' of debris that builds up on the pintles over several years, which then alters the spray patter or something, not sure. Either way, these sodding engines need injectors every 80-100K regardless to keep them running well.

[SANDEGTI]

I stopped using the Liquimoly as I found myself putting a can in with every refill to keep the idle smooth.  It was becoming an addiction.....I could see myself being a 3 cans a day man 

When I stopped using it, the idle got rough as a badgers arse for about a month, but then smoothed out again.  I think that cleaner removes a 'cushion' of debris that builds up on the pintles over several years, which then alters the spray patter or something, not sure. Either way, these sodding engines need injectors every 80-100K regardless to keep them running well.

Sounds like you need to lay of the Liqui Molly for a little bit 

I've never been so disappointed, it never arrived today. Supposedly coming tomorrow but I'm worried if I'll become an addict if this stuff is as good as they say it is. I've seen a video on how it works, the guy put it straight through an injector and it started cleaning it up pretty quickly, before it was just spraying in a straight line but afterwards it was more spread out and consistent. A bit like when you change the shower head after a few years 

Apparently it continues to clean them way after you put it in so might explain why it got smoother after a month?

[pudding]

Yeah, it's cheaper to drink beer 

I should clarify.....the idle got rough again when I went to LiquiMoly Anonymous for a month, but then smoothed out again whilst still sober 

[SANDEGTI]

Yeah, it's cheaper to drink beer 

I should clarify.....the idle got rough again when I went to LiquiMoly Anonymous for a month, but then smoothed out again whilst still sober 

Well done for sticking it out.

Well, the magic liquid came this morning and as soon as I finished some work we put £40 in and put it in right after. Gave it a bit of a beating on the dual carriage way, stayed in 5th gear for most the way at 3.5k revs with little stops for about 45 minutes. I must say for the first time in MONTHS, we pulled over to Lidl and the car wasn't jumping about like it normally does. Usually it's fine when cold but as soon as it gets up to temp it idles a bit funny. The car was hot and no issues in that respect so what a result 

Not the only thing I noticed, I swear the car has got quieter. At 4k revs it now sounds like what it used to at 3k revs if that makes sense? And the placebo is strong, the car is picking up quicker 

OP, would 100% recommend this for £7. Even if it doesn't fix it in the long run at least you know what the issue is. Surprised by the results so far.

[pudding]

Another satisfied customer    It seems to work a lot of people. If there's no difference, the injectors are fine.

Watch that smooth idle habit though, it gets addictive 

Mine's the same. Pulls like a train when it's cold but the more miles I do and the hotter it gets, the worse the idle and low end pull get. I know what you mean, the engine does run a heck of a lot quieter and smoother when the injectors are working properly.  Unfortunately, it doesn't seem to last.....hence my Liquimoly addiction    Still, it's a good band aid until you get around to a walnut blast and injector replacement.

[SANDEGTI]

My partner thought I was mad (she's not wrong) when I said I ordered injector cleaner. I've been going on about it for the last few days and I think she's getting sick of me. I just told her it's £400 for new injectors or Liqui Molly once a month for a year, up to her now 

I'm gonna keep an eye out on the MPG to see if there's any improvement there.

In your opinion, is it worth getting the inlet cleaned? I only ask because I'm planning a trip to R Tech in the next month or so. I've read a lot about it and everyone says it comes clean but can't notice a difference. Is it just a maintenance thing?

[pudding]

Haha, my missus's eyes glaze over whenever I talk about the car, followed by a big yawn    Injectors are £200 each for mine 

I can't say I noticed an mpg improvement using it but 35-40mpg is easily achievable anyway if driven gently enough.

Carbon build up can get bad enough to cause warmup misfires, but if yours is smooth when cold, I wouldn't worry about it for now, but definitely get it done whilst the inlet manifold is off during injector replacement 

AKS Tuning did a walnut blast on mine, must be getting on for 4 years ago now, and I can't say I noticed anything.  They did say my valves weren't as bad as most they see, so that could be why.