Boost hesitation under acceleration through every gear

[Tha_Don]

Hi All,

The other day whilst driving on the motorway in my 2007 MK5 GTI I had a very noticeable intermittent loss of power (no turbo). I noticed this just as I was coming up to the junction that I needed to take. I stopped at the traffic lights, pulled off and then through every gear it was hesitating when the turbo was kicking in, kind of felt like it was kangarooing.

I first started to notice this on cold starts but as the car reached up to temperature, it ran fine and I had a smooth boost through every gear but now this is happening whatever the temperature is.

I did a lot of reading about this using the search function on the forum but cannot find anyone or anything who has had the same problem.

I have no CEL light but I had the car plugged in to a Snap On Ultra diagnostic tool and it showed a fault with MAF sensor. I didn't get the fault code cause I wasn't there when it was plugged in.

As a result of this, I thought I would carry out the MAF sensor test by unplugging it and driving around but there is no difference whether it's plugged in or not. This has made me think it's not the MAF sensor although the diagnostics said there was. I thought by unplugging the sensor would have improved it by a little bit but no difference at all, just a CEL from driving it round with no sensor plugged in 
I have also done the PCV test and that's seems fine. I have recently put in a rev G DV from a rev D so I know that is fine. I have checked for any pipes that have come loose on the turbo but all seems fine. Intercooler hoses also seemed fine although there was a little oil/gunge underneath the pipe which could potentially be a boost leak?

So to conclude, I don't know whether a new MAF sensor would be the cure of the problem? I don't want to have to fork out for a new MAF sensor if it's not going to fix the problem.

Any help would be greatly appreciated.

Thanks in advance.

[Tortaruga]

Are you running an aftermarket intake?

[Tha_Don]

Thanks for the reply.

No, I have the standard air filter with engine cover.

Forgot to mention that when I give it hard acceleration, there is a loud hiss.
I have inspected all pipes coming from the turbo and they all seem fine unless its something I can't see.

I was thinking that it can't be my DV as ive already changed it for a rev g about 3 weeks ago. When I took it out to check it, it looked fine.

The fault code is p0100 -  Powertrain - Mass or volume air flow circuit.

Ive disconnected the MAF lead from the sensor, tried driving it but there is no change!

Dont know what it is! Im completely stumped!

[Tortaruga]

I'm pretty sure that if you unplug the maf it affects the idle. If there is no change the maf is bad.

I'd wait for a few other members' opinions before shelling out for a new one though, as I'm not an expert.

[Tha_Don]

Yeah when I unplug the MAF you can hear a slight change in engine noise, so your right, it does affect the idle but drivability wise, it drives like sh*t when MAF is plugged in or not plugged in.
 
Also, I don't think that a bad MAF can cause a loud hiss under hard acceleration. Although it is running very lean as the fuel is dropping down very quickly. Maybe a combination of a bad MAF ane something else? I just don't know!

Many thanks for your replies tortaruga 

[karl210]

Idealy you need someone with vcds, will save you time and money, or even buy one they really are worth it in the long run for around £150. Have a look on the vcds regester and see who is close to you, where abouts are you? sounds like a vac/ boost leak to me.

[Itguy]

Hole in the intercooler? Cracked turbo?

I think the maf will be a red herring here as if you've got a big boost leak then the engine won't be getting the right fuelling regardless of what the maf wants to suggest.

It's the hiss that needs sorting first then take it from there.

Have you got a method of putting pressure in the system with the engine off? Mityvac etc? To help find where the leak is?

[Tha_Don]

Idealy you need someone with vcds, will save you time and money, or even buy one they really are worth it in the long run for around £150. Have a look on the vcds regester and see who is close to you, where abouts are you? sounds like a vac/ boost leak to me.

Im in leicester karl but I think I may have temporarily sorted it 

It was getting to the point where I've had enough so I ripped off the engine cover, started the car up, stuck my head under the hood and started fiddle with all turbo pipes/vac hoses to see if any were loose. Checked all turbo pipes (for the 100th time) and everything was tight and not moving. I've had it on the ramp no end of times and also inspected piping from underneath and everything seemed tight. I didn't think that any of the pipes would be loose as I changed the engine for a BHZ and used loctite on all screws so I kind of knew already it wouldn't be any loose screws. Intercooler hoses seemed fine as well.

So back to under the hood I started to look towards the VAC pump, moving the pipes around and found a push pipe that was split at the join to the vac pump. I fiddled around with it and it  was hissing like a mofo! I thought this must be the culprit so I decided to get the duct tape out put a piece round the split, moved the pipe around until it no longer made a hiss, took it for a drive and hesitation had gone! 

Still can hear a slight hiss under acceleration but no more hesitation. There seems to be quite some lag aswell but think that may be due to me taking the first part of the air intake off for testing.

I do however still need to get it tested. Tried calling RTech as they do smoke testing and they are only 15 miles up the road from me but they never answer the phone 

Thanks guys

[JagGTi]

Let me know if you get this sorted mate. Im also in Leicester and seem to have a similar problem or some sort of boost leak somewhere!

Trying to get in contact with rtech today but no luck.
They are normally quite busy and have a few weeks wait so might take a trip down to aks in bedford instead where I normally get it serviced.
Dont know of anyone decent here. You tried nasstech in thurmaston?

[Tha_Don]

Let me know if you get this sorted mate. Im also in Leicester and seem to have a similar problem or some sort of boost leak somewhere!

Trying to get in contact with rtech today but no luck.
They are normally quite busy and have a few weeks wait so might take a trip down to aks in bedford instead where I normally get it serviced.
Dont know of anyone decent here. You tried nasstech in thurmaston?

Sorted it mate, think it was a loose connection to the coil and that split pipe to the vac pump. Not getting any hesitation anymore.No not tried nasstech, are they vw specialists? What symptoms are you getting?

What colour is your gti? May have seen you about 

[JagGTi]

Il have to check there, pretty sure it will be a similar issue loose pipe/crack. Well hopefully nothing serious atleast!
Candy white black wheels 3dr. How about yours? Il keep an eye out

[Tha_Don]

Il have to check there, pretty sure it will be a similar issue loose pipe/crack. Well hopefully nothing serious atleast!
Candy white black wheels 3dr. How about yours? Il keep an eye out

Yeah shouldn't be anything major, just inspect all pipes/hoses etc, should be something to do with that. Get it on a ramp, that will be the best thing.

Kool. Mine is red with grey pescara's, also a 3dr.