My Octavia VRS starts absolutely fine, and has a perfect idle unlike all the previous similar posts I can find.

The car pulls away fine initially, but when accelerating up to around 2,000 revs It starts jumping about and is hesitant until the turbo spools up and all is clear. It’s then clear for the rest of the drive.

I have changed the coolant temp sensor so far, but wondering what to check/change next without spending a fortune.

I wouldn’t describe the hesistance as a misfire- It feels more like a sensor issue.

What other sensors could this be?, and any way to check them.

Also:- no fault codes stored. And the car has been remapped(not recently)

Many thanks

Do you have clean AIR filter?

Faulty N75 valve?
Can you do log of turbo pressure + MAF + RPM?

Yes the air filter is clean but would this only affect it whilst cold anyway?

no idea what the n75 does but I’ll look into it.

As for logging turbo pressure, MaF and RPM, I have no means of doing this. I only have a simple code reader.

A budged Bluetooth ELM OBD2 scanner + torque on Android can do the trick. 

N75 is valve sitting next to the air filter. It's job is to operate with wastegate - protecting the engine from overboosting and helping to regulate turbine speed. If you find it, check the number on it. Most aggressive ones ending with F if I remember right prone to overboosting issues on very cold starts, throwing engine into soft-limp mode.

Ok so would this be a case of cleaning it? Replacing for another f code one or an alternative?

Thanks

Well if it's common winter cold start overboosting it should be ok if you let it idle a bit and not go hard first 1-2km. Agressive N75 is not a big issue, this setup just don't like very cold start.

Log of turbo boost / ignition / retard during the issue will be very helpful. Unluckily I'm from Czech rep., so I cannot offer you my services :-/

Ok I have a Bluetooth obd thing somewhere, so I’ll try and get that info too.

Ill have to use my child’s fire tablet as that’s the only android in the house. Any ideas on a good app for it? Preferably free. Edit....... I have just found it it is a 327 elm mini.

cheers

Edited 12 January, 20197 yr by 4Wardy

Look for Torque app. Pro version is very cheap.

Ok, tried all apps I can find and none work. Can’t get torque because the tablet is amazon fire.

I also should mention that the car isn’t great on fuel and always seems a little smokey when at idle.

Colour of smoke?

White

Losing water?

 

Nope. I know you are thinking head gasket.

i was thinking perhaps it’s overfuelling?

Could it be the secondary air pump thing?

when I start it if I pull the hose off the air box I can feel it sucking my hand though!

Just looked at the n75 valve.

its number is 058906283F

Yup, F one can do the stuttering when cold (it give agressive turbo kick, when cold outside it can bit overboosting).

 

But, we need MAF/MAP/Lambda data during the hiccup to tell what's wrong.

 

Sometimes this can be caused by bad breather hoses and bad PCV hose/valve also. 

Ok I’ll try and borrow an android device from someone and get some info. Will it log the info or do I have to get it live when it’s doing the problem?

Also, this y-piece (right in the middle of the picture) is extremely soft, is that normal? Looks like some sort of breather. - I know hoses can collapse causing issues etc.

Edited 13 January, 20197 yr by 4Wardy

1 - breather hose which usually cause problems, not rly expensive one, expect to be full of oil and cracked in the Y shape or under.
2. Under this is N249 and lots of vacuum pipes, which usually collapse also and create bunch of stuttering.
3. Just under the oil level pipe is PCV breather hose + valve, which usually is fcked up also and can cause oilo consuption + erratic run under load. Pain in the ass to change it, but it worth every penny.,
 

PCV schematic here

The Y shape breather hose is 06A103221BH

Could that y hose be the problem then? Is it normal to be super soft or should it be firm?

Ok, so I have A quoted an android tablet. I’ve got torque and it connects to my obd dongle.

i will download the pro one shortly now I know it works.

what gauges shall I put on the screen and how do I log/store the data?

thanks

MAF/turbo pressure/rpm/coolant temp/ air/fuel ratio

How to store data - dunno I use regular VAG.COM to do that, but there should be some option. 

 

For example healthy MAF should read max 2.7g/s on fully warmed engine without acc on.

Ok I’ll try and work out the storing of the info.

i was able to watch the garages whilst driving to a degree I noticed the maf was 4.8 when off throttle and I think I saw 6.something.

boost when flat out was about 15 psi but I did see 42psi.

maybe that was a bum reading though.

will set it up and try in the morning when the car isn’t behaving!

Cheers

Anything more than 3g/s without acc on and fully warmed means that your MAF is on its way to motor heaven. 

35+ psi for longer time means that your car is chipped or heavily overboosting.

Anyway if the MAF is shot, it's possible that it cause overfuel at cold motor condition. Got similar issue with my RS last year, new one from bosh made the car more powerful and smooth.

Max reading of MAF at VOT approx 5000rpm at 3rd gear (warning, highway needed for this) should be approx 150g/s ( 80% of horsepower).