VRS hesitation...help needed!

[JMvRS]

Hi all. I've had my 05 plate MK1 VRS for almost 2 years and had the following problem ever since.

 

On part throttle acceleration it has a hesitation which I can't get to the bottom of to date. It feels like a lean mixture and according to a live data run with vagcom it has just that....the lambda reading fluctuate's all over the place.

 

When accelerating hard it's mostly less noticeable but can always be felt. If pulling away sensibly on a part throttle at its worse it can feel really hesitant on and off as the throttle is squeezed in to full throttle, then once it hits 4000 it almost runs without fault and pulls strong. This always happens at 4k only and during medium to hard acceleration....never any other rpm...it's almost like a switch has been flicked. Yet on A road or motorway speeds around 70-75 at part throttle at less than 4k....around 3k is... it will pull past traffic with little extra throttle and hardly noticeable hesitation, but as soon as you come to a stop and pull away again the hesitation is clearly there back up to 4000.

 

To date I've changed the following common parts after all the 1.8t fans on planet Google say "oh it's.....that's really common"!

 

Plugs...twice...NGK.

Coil packs...new genuine Bosch.

Lambda sensor...new genuine Bosch.

Airflow unit....New genuine Bosch.

Genuine VW main dealer coolant temp sensor.

Genuine VW main dealer dump valve.

Cleaned and re set the throttle body (it was spotless inside but did it anyway).

Cleaned all electrical plug connection's with electrical contact spray including the earth on the cam cover.

Replaced the split Y breather at the top and the split vac hoses under the inlet plenum.

Carried out a smoke test...not a wisp of leakage anywhere.

Fixed minor exhaust leaks...totally leak free now.

New fuel filter...old original was still fitted date stamped 10/04!

Carried out a couple of oil and fliter changes with decent or O.E oil.

 

And breathe!

 

Yesterday I hooked up a boost gauge to see if it fluctuated when the hesitation occurs but it boosts to just under 10psi quite quickly and holds it firmly....tho I think from what I understand that's a bit low as it should be around 11.5?

 

I've put on 22k of its 147k total in almost 2 years and would ideally like to keep it as it's a decent car but it's driving me mad!

 

I'm tempted to change the fuel pump, regulatr or N75 valve next but I'm board playing parts roulette and would ideally like to get a positive direction before adding to the parts list.

 

I've also cleaned out the pressure regarding housing after a friend in the trade said they can suffer from the fuel hoses breaking down with age. I did find some traces of that so perhaps that's the next direction. I've also been pointed towards the boost pressure sensor on the intercooler as maybe a fault.

 

There are no fault codes stored as checked on vagcom, snap on and Mac tools scanners. I've also disconnected the battery at one point to try a major re set as I was told they are a learning type ecu.

 

One of the weird things I think happens is that when changing some of the parts....breather hoses, plugs, coils, Maf etc I was convinced it felt better for a number of miles only to return again....although it could have been wishful thinking but I'm fairly sure it wasn't.

 

So....any advice would be greatly recieved! I'm not totally stupid with cars as Ive worked with them all my 34 year working life but this one has me stumped.

 

 

[JMvRS]

Shameless end of the year bump time!

[Saints92]

Could be a leaking injector. Seen BMWs with similar symptoms and that's been the issue. Can be hard to diagnose without finding someone who can test them. 

Edited 1 January, 2018 by Saints92

[chrisw3205]

My mk2 tsi has just been diagnosed with a faulty injector by a specialist garage. My symptom was stuttering/ hesitation under light throttle. Seems exaggerated in this cold weather and disappears under hard throttle. When they connected it to the computer, no fault codes are showing. However looking at the details for the injectors, one was dumping fuel in. Could be worth looking at this. Not the cheapest to do a trial and error on, so find someone that has the software?

[JMvRS]

Thanks chaps and a very belated happy New year!!....i don't get out much...well...away from the workshop.

 

I had the injectors cleaned through last week on a proper machine and all are spraying fine. Some small bits of rubber were noticed in the tops so I replaced both the inlet and outlet fuel pipe from the rail and cleaned and blew that out too. I fitted a new Bosch pressure reg and changed the N75 valve for good measure with the latest Genuine superseded unit.

 

It boosts better/smoother now in the zone it always ran well in but the very light throttle/low speed hesitation is still there. Fuel economy is 26-28mpg shuffling around and 34 with some traffic and a lot of A road use @ 70-80....so 80-90% of the time it's doing all I'd expect of it, but the last 10-20% of the time it's just frustrating. 

 

It feels like a throttle pot that's worn in the initial application/first 1/4 throttle zone....maybe a new throttle body needed? 

 

Any more help / ideas much appreciated...im not planning giving up just yet but it's testing my enthusiasm for an otherwise good driving car.

[octaviavrs170]

Hi bud I have a very similar problem.

I think all these engines have a hesitation point tbh don't know why but I love mine and it's worth the aggro. Btw how do you clean out side mounted intercooler. What do you use to clean it out. 

Edited 23 May, 2018 by octaviavrs170

[penguin17]

Initial thoughts: 

 

• MAF sensor - I think this will happen at high revs and they are prone to failure at higher mileages, VAG recommend changing at 80K IIRC
• Diverter Valve - again, prone to failure even on stock cars

 

EDIT: Sorry, I just spotted you'd replaced the MAF sensor 

Edited 24 May, 2018 by penguin17

[David 8]

I'd be looking at the fuel pump next. Got one you can borrow, easy to swap out. 

[JMvRS]

On 23/05/2018 at 18:15, octaviavrs170 said:

Hi bud I have a very similar problem.

I think all these engines have a hesitation point tbh don't know why but I love mine and it's worth the aggro. Btw how do you clean out side mounted intercooler. What do you use to clean it out. 

You have my sympathy!

 

I understand these engines have some in-built ignition timing/torque control  maps which are supposed to help them drive smoother when new but can play up as time/mileage rolls on due to the calibration...maybe I'm chasing something that's a problem in the basic O.E mapping.

 

I always planned to increase performance a bit...not a whoosh bang lotsa wheel spin big pub talk number but a sensible linear increase for a strong driving road car...but I want to get to the bottom of the problem first rather than risk compounding the issue incase it's something like a weak fuel pump/electrical problem or something like that.

[JMvRS]

On 24/05/2018 at 14:15, penguin17 said:

Initial thoughts: 

 

• MAF sensor - I think this will happen at high revs and they are prone to failure at higher mileages, VAG recommend changing at 80K IIRC
• Diverter Valve - again, prone to failure even on stock cars

 

EDIT: Sorry, I just spotted you'd replaced the MAF sensor 

Yep....done both of those but thanks for the input....keep it coming...

[JMvRS]

On 26/05/2018 at 01:54, David 8 said:

I'd be looking at the fuel pump next. Got one you can borrow, easy to swap out. 

Thanks I'll bare that in mind. It has crossed my mind....i actually bought an alleged new old stock unit from that famous used parts site on the interweb but it turned out to be not so o.e as the bit of old Bosch box stuffed in packing suggested...and it rattled!....the vendor did give a full refund to be fair but buyer beware!

 

On reflection though I figured if the pump was playing up it would effect power higher up when the demand for more fuel was greater?....or is there some form of damping in the pump?....i changed the pressure reg in the fuel rail thinking that could have been an issue....particularly after I found the rubber particles in the rail.

 

I've just been pointed down the N249 valve route. Apparently it feeds through the DV circuit and can flutter when old and weak and subsequently cause an issue to the DV which then pulses and fluctuates boost....or something like that.....god give me a pair of 45 webers and a distributor!

[David 8]

33 minutes ago, JMvRS said:

 

On reflection though I figured if the pump was playing up it would effect power higher up when the demand for more fuel was greater?....

 

 

Bingo, thats what mine did, over about 3.5k and thats when it showed it's age, boost would go all over the place, no codes in ecu, no other clues either. 

[JMvRS]

Ah mine runs good over 4k....its at low rpm part throttle it's worse.

 

I've just bypassed the N249 valve....or at least I think I have....by running the DV feed direct from the bottom of the plenum. Appears to be a tiny bit more responsive but the low rpm/20% of throttle still brings the hesitation to the party.

[fwdnewbie]

Personally I'd remap it, that way any lean running could be tuning out with a new fuel map.

Most cars have a flat spot somewhere in the rev range as a way of getting through the emissions at the time of leaving the factory.

 

The Mk4 Golf V5 engine has an awful one. 

Get it mapped out and have a smoother power curve throughout the rev range

[JMvRS]

That is the plan eventually, It's more than just a flat spot though. There's a distinct "on/off" hesitation on light-1/4 throttle acceleration. If I pull away lively/hard it's less noticeable but always there lurking in the power delivery...i don't want to waste a mappers time and effort trying to dial out a problem by taking them a car with a fault that's hardware related. 

 

There's also....on occasion....a distinct power cut when lifting off the throttle...like it's suddenly sucked in a tennis ball through the intake and choked on it!....it doesn't do that every time on lift off though....once in a blue moon...like this morning!

 

I'm steering towards a fuel pump or throttle body change at the moment...though I don't think the pump is the cut/choke issue.

Edited 5 June, 2018 by JMvRS

[Passeyfier]

My VRS estate has a slight throttle hesitation too but, like you said, seems to only be prevalent on light throttle and lower down the rev range. If I'm steadily following the flow of traffic and suddenly need to accelerate a bit there is a hint of hesitation below 3k but it doesn't bother me too much as a quick downshift and depression of the throttle seems to sort it out for the most part. I guess it's just something to be expected on a higher mileage example. 

[JMvRS]

That "sometimes" works for me too (though i try to avoid looking like a middle age boy racer in a bright red car racing up behind someone..."just clearing a running fault honestly"!), but more often than not trying to accelerate through the problem makes it worse until it hits the 4k mark...then it's literally like a switch is flicked and another engine has kicked in with no faults at all!....though sometimes it can still be detected just as it pulls around from 4 to 6k.

 

Even more bizarre is you can drop below the 4k zone....say 3k steady/light throttle @ 70-75 in 5th, squeeze the throttle in all the way to full throttle and it just boosts and goes with no hesitatation.....stop at a roundabout or junction to pull away again and it'll play up right through previous good 3k zone and run fine past 4k again....i just don't get how it can be a barsteward pulling through 3k through the gears yet fine pulling through the same rpm/throttle position/load in 5th....and sometimes it's less noticeable than others driving in the same way/load conditions. 

 

I'm sure the answer is staring me in the face....itll be a good day when it's finally cured as there appears to be a few of with a similar/same fault to a lesser or greater degree.

[octyal]

It may not be relevant, but something i have noticed with mine is that it feels quite flat when pulling away - especially on slight gradients - requiring a slightly harder press of the throttle. This led me to check the throttle % using my trusty hand held scanner (you can use torque pro and vcds) . It starts with a reading of 3-4% (i think, it has been a while since i looked) then as you start to press the throttle pedal down, it drops to 1-2%, then as you keep pressing it goes back up again. This made me wonder if that is why it feels flat when  initially pulling away from a standing start. Certainly worth looking at, not sure if it is the same across all cars, as i don't have anyone local to check it against.

 

Found the original post i put up about it here

 

[JMvRS]

Cool thanks for that. I've got a snap-on solus....on that the live throttle readings with the engine off gives two reading....one high and one low...they pass each other as you open the throttle but never show 0% when closed or 100% when open....ill do it again and note down the readings.

 

Mines not so much a flat spot but an on/off trys to go/hesitstes/trys to go/hesitates repeats until 4k then pulls clean.

[octyal]

11 minutes ago, JMvRS said:

Cool thanks for that. I've got a snap-on solus....on that the live throttle readings with the engine off gives two reading....one high and one low...they pass each other as you open the throttle but never show 0% when closed or 100% when open....ill do it again and note down the readings.

 

Mines not so much a flat spot but an on/off trys to go/hesitstes/trys to go/hesitates repeats until 4k then pulls clean.

 

That does sound alot like the N75 playing up. Do you still have the SAI attached? I have heard of that causing similar issues

[David 8]

TB reading sounds good to my distant memory,  I'd seriously rule out the fuel pump, they are now at minimum of 13 years old some as much as 18 years old. They ain't built to last, do you know anyone with an 1.8T golf or Leon you can do a swap with, they are a piece of **** to change. I farted about with mine so many times I had it down to about 3 mins to change one. All a long time ago now though. Other than that I can think the mapping may be playing up, are you all standard maps ? Stuff like N249's and N75's are almost never at fault, loading up the parts cannon gets expensive and never really fixes these weird no code issues. 

 

Another thought, coil pack wiring ?? 

 

You can log AFR which may give a clue, this can be done with torque app. 

 

There was an issue years back with the standard maps which IIRC Jabbasport uncovered the problem, that was about ten years ago. 

 

 

Just for info here, mine got sold when on 180k, hardware was original except coils and DV, all the other bits, N249 and N75 were fine at that mileage, 

 

 

Sorry this is a bit disjointed. I'm brain storming an old subject here lol 

 

 

 

My bible during 1.8T days https://drive.google.com/open?id=1gLa-cPJs8Z3EUmFYzbDXCDWQcLwLl7bm

 

 

[JMvRS]

16 hours ago, octyal said:

 

That does sound alot like the N75 playing up. Do you still have the SAI attached? I have heard of that causing similar issues

I thought similar....fitted a brand new genuine N75 two weeks ago....still the same.

Yes SAI still fitted. I have wondered if there's a leak there....though a smoke test hasn't revealed anything from anywhere.

[JMvRS]

16 hours ago, David 8 said:

TB reading sounds good to my distant memory,  I'd seriously rule out the fuel pump, they are now at minimum of 13 years old some as much as 18 years old. They ain't built to last, do you know anyone with an 1.8T golf or Leon you can do a swap with, they are a piece of **** to change. I farted about with mine so many times I had it down to about 3 mins to change one. All a long time ago now though. Other than that I can think the mapping may be playing up, are you all standard maps ? Stuff like N249's and N75's are almost never at fault, loading up the parts cannon gets expensive and never really fixes these weird no code issues. 

 

Another thought, coil pack wiring ?? 

 

You can log AFR which may give a clue, this can be done with torque app. 

 

There was an issue years back with the standard maps which IIRC Jabbasport uncovered the problem, that was about ten years ago. 

 

 

Just for info here, mine got sold when on 180k, hardware was original except coils and DV, all the other bits, N249 and N75 were fine at that mileage, 

 

 

Sorry this is a bit disjointed. I'm brain storming an old subject here lol 

 

 

 

My bible during 1.8T days https://drive.google.com/open?id=1gLa-cPJs8Z3EUmFYzbDXCDWQcLwLl7bm

 

 

That's great thanks....no info is bad info...brain storming works.

 

I've got a new pump I bought off eBay a while back....alegedly a NOS Bosch unit but it has a rattle so I never fitted it...plus there's no Bosch logo marking on it anywhere...but I guess there's no harm trying it to see if there's any change at all. I see the pump is under the seat when I went part number hunting so looks simple to swap.

 

 All totally standard to the best of my knowledge. The previous owner had it from about a year old and 8k....i bought it 2-1/2 years ago with 125k...now on 150k....no mention of re mapping which most like to claim if it's been done....my good lady can run side by side up to 120 (on a private road of course!) with her standard 140hp 2ltr Tdi mk2 octy so I'd be surprised if it's anything other than stock.

 

I've heard of the coil pack wiring...going brittle with the heat?...was told that part of the harness use to be available but not anymore allegedly....not looked into that myself but considered getting a friend whose good with wires to make a new one. Don't the TT's have an o.e heat shield in that area?

 

I fitted the new N75 a couple weeks back after the boost started to "waive" up and down under load...could hear the turbo whistle up and down up and down....the new N75 cured that but not the other issue. 

 

I've considered a mild re map from either Rtech, Jabba or Bill @ Badger5. I did email Nick @ Rtech who believed he could find the problem but didn't want to speculate....which is fair enough as it's their living....but I don't see the point taking a poor running car to them and ending up with 1k bill for a 300 quid remap if it's a job I can fix first for even a couple of hundred quid. I figured there's got to be a solution out there with the amount of 1.8t powered cars around that someone must have come across this in the past.

 

I'll take a look at the 'bible' thanks!

 

[JMvRS]

Well the management light finally came on last week....1st time ever since I've had the car/problem.

 

The hesitation was getting more like a misfire and a scan showed up the SAI pump....at last a positive direction!

 

Erm...no. The seal on the pump was indeed hanging out due to a couple of broken rivits. We by-passed it for now and made a blank for the head. Code cleared and no more misfire....but the bloody kangaroo hesitation is still there!....so we can ad / tick off the SAI pump to the list as not the hesitation fault.

 

I'm wondering if it's the flip side to another fault that comes and goes. If I catch the throttle in the right place just lifting off slowing down or changing gear it feels like it's cut all power and hit a brick wall at the same time. Then as the throttle is re applied either in the same gear or after another has been slotted in it just picks back up like nothing has happened. I'm wondering if the hesitation under part load is the opposite to whatever is causing the lift off cut if that makes sense.

 

Anyway...the search continues....

[David 8]

3 hours ago, JMvRS said:

 

 

I'm wondering if it's the flip side to another fault that comes and goes. If I catch the throttle in the right place just lifting off slowing down or changing gear it feels like it's cut all power and hit a brick wall at the same time. Then as the throttle is re applied either in the same gear or after another has been slotted in it just picks back up like nothing has happened. I'm wondering if the hesitation under part load is the opposite to whatever is causing the lift off cut if that makes sense.

 

Anyway...the search continues....

 

 

That sounds like what happens when the brake light switch is knackered. car thinks you are braking and cuts power.