Passat PD130 - Hesitancy when accelerating

[andysills]

Hi all,

I have a 2001 Passat PD130 SE which I have owned for six months. It’s an ex company car with 99k on the clock and a full VAG SH. I am really pleased with it BUT I have a slightly annoying problem:

The problem is that I always get a ‘hesitancy’, or ‘intermittent power drop out’ at low rpm when I accelerate.

It’s only noticeable when accelerating (normal driving conditions) in first, second or third. It occurs after a gear change when the rpm is still relatively low. I.e. I change up and begin to accelerate whereupon the engine seems to stop pulling for a fraction of a second before the acceleration carries on again. This only happens at low rpm and only happens for an incredibly short (but noticeable to my and my passengers) space of time. I have taken it to Peter Cooper VW in Southampton and they said that “there we no fault codes” in the system, but that they could plainly see the problem during their road test. A technician and the foreman both took it out for independent road tests.

They said that I could go on changing parts and spending lots of money before isolating and fixing to cure the problem. They advised me to wait until the problem gets worse so that some fault codes would show up. It is something that I would really really like to fix but having reviewed the posts on this site I seem to be the only one with this problem. Apart from that the engine pulls strongly and fuel economy is good (average 48-50 mpg)

Has anyone had a similar problem ? Any help or advice would be greatly appreciated.

P.S. It is getting serviced in a few weeks by VW in Salisbury –so I’ve asked them to have a look at the problem but am not keeping my hopes too high.

[shark_90]

I'm guessing it's at about 1800rpm.. my PD130 A4 does exactly the same thing. It accelerates through 1800 without a problem, but if it's at 1800 when you apply power there's a hesitancy for about a second or so before the power comes in?

[Waitey]

Mine had the same problem, I had the MAF changed and it is fine now. There are loads of posts on MAF's on the site. Most people suggest asking your local VW dealer for a replacement (reconditioned) one to try on a sale or return basis to see if it is that. They are I am told easy to fit, again check previous posts on MAF problems. Hope this helps

[shark_90]

I'm not sure this is the MAF.. I know mine isn't anyway. A MAF problem would be problematic throughout the rev range and be constantly low power. And you're right they're dead easy to fit, if it is that.

The common test to see if it is the MAF is to disconnect it and drive the car. If it's better (or no worse) then it's the MAF

[andysills]

Thanks Bigal and Shark,

Shark your description of the problem is spot on. I'll talk to VW about possibly swapping the MAF out at the service (trial only!). I was also considering getting the engine re-chipped (Dragon digital or PSI powerbox) but thought that this would exaggerate the problem - hence my need to fix if first. How does your upgrade affect the hesitancy issue Shark? - and which chip did you go for? (meanwhile I'll read up some more on the MAF's)

cheers

Andy

[shark_90]

Andy

The MAF won't help you I believe, as I say mine does this and my MAF is fine

I wouldn't say that a tuning box would exaggerate the problem, I can't say mine's any worse with than without. I went for the Alpin PD-4 box, but not by choice really. It was on Ebay, and although I'm quite weary about buying "decent" things (ie things I'd plug into my beloved car!) I did a lot of research and the one I bought is manufactured in Germany and is TUV approved and supplied through a reputable dealer in the UK. Also, the original reciept was included in the transaction for £600, and I paid just over £200 so I did well.

I've heard good things about the Dragon boxes, and PSI and Tunit have also been highly spoke of.

If I were you I'd go for a digital box. I tried an analogue box and found the digital to be much more predictable and "useable" if you like. However, if you have the money to spend, I would definately go for a remap. I did a lot of research into this and I didn't/don't really have the money to spend at the moment, but I will do as soon as I can afford it.

I've also heard (although can't confirm it) that a remap DOES cure this hesitation problem. There's hope yet!

And I must say, I'm pleased to hear of someone else with this problem. It's damn annoying isn't it!

[Wobby]

I have the same age passat as you with 140k and it doesn't hesitate, but i do have a MAF problem.

For what it takes (and knowing the MAFs are a weakness) the dealers ought to change it and give it a run. Sounds more sense than driving it and saying "its got a problem" but not knowing how to fix it.

I think it could be the MAF, ask the dealers if you can exchange under the condition that you exchange back afterwards if it doesn't solve the problem. Is the airfilter new(ish)? is the bottom of the filter housing clean? Worth hoovering it out and changing the airfilter its not been done recently.

You are getting it serviced at VW!!! Wow!

RobK

[Wobby]

[ QUOTE ]

A MAF problem would be problematic throughout the rev range and be constantly low power.

[/ QUOTE ]

Mine has a MAF problem, doesn't have constant low power, i didn't think MAF problems would cause similay problems throughout the rev range?

[Rustynuts]

Shark, you seem confident that this problem is not related to your MAF. How can you be certain? MAF's fail in many ways, usually without throwing a fault code, and specific revs problems are fairly common (though usually about 2600 to 2800 rpm). Without plotting your MAF values when new and comparing them when you suspect a fault, the only other way to tell for certain is to replace it with a known good one.

The R32 boys (and girls) have had success with remaps fixing hesitation issues, and VW released a software update for the R32 which also fixes their particular issue. I've heard of no instances where a remap cures a hesitation fault on a TDI, only exagerated problems. I'd recommend leaving the remap until the underlying problem is fixed, certainly if the remap is tuned to your car. An "off the shelf" remap will possibly be more forgiving with a problem but a custom remap will account for the fault, and the tuner will attempt to straighten things out with the software, then when the fault is finally fixed (whatever it may be) the remap is nothing like as good as it should be.

[Rustynuts]

[ QUOTE ]

Is the airfilter new(ish)? is the bottom of the filter housing clean? Worth hoovering it out and changing the airfilter its not been done recently.

[/ QUOTE ]

The seal on the air filter isn't meant to be reused. It's designed as a once only seal and if opening the airbox and resealing it, the seal will be compromised and may fail.

[Wobby]

Thanks Rusty.

Do you mean the seal between the top and bottom half of the filter?? I only use copy filters so i dont get the box seal.

I think my next one will be from the dealers, but i will have a look to assess if it looks to be sealing ok.

I have logged my MAF readings and got a max reading of 1200g/s regularly, even though the expected maf is 850g/s

I logged a Skoda VRS and it only generated a MAF reading of 850 under hard acceleration. I am sure my MAF is faulty, strange that it seems to be reading too high not too low. I guess that could explain why i am losing some fuel economy.

EDIT !!!! oops, all reading above are in mg/str not g/s

RobK

[Rustynuts]

The box seal is part of the air filter. It's the rubber seal you see pictured here in pink.

[Wobby]

Ahh.. ok, yeah i do change that every 10k.

I find it amazing how much crap is in the bottom of the airbox! If you dont clean it out it must just suck back onto the bottom of the new filter and its already partly blocking straight away.

I dont think the dealers bother. When i got the car it had been dealer serviced and it had 2cm of crap in the bottom of the airbox. Its never had that much since, although i do change it more than necessary.

RobK

[shark_90]

Fair enough Rusty.. only repeating what I have been told by other people on the forums. I'm pretty confident my MAF is absolutely fine but I do get this slight hesitation in every gear at exactly 1800rpm. I have looked through posts on here regarding it and it seems to be common in PD diesels, as is MAF failure. However many posts have told me to unplug the MAF and if it's better or no worse, then it's the MAF. Which it isn't, it's like driving without a turbo completely (just like my MG 2.0 TDi was after losing the MAF on that, and my colleague's PD130 Passat when his MAF failed).

I'm probably wrong, but after all the advice I have been given on here it doesn't sound like a MAF to me. Basically what I was trying to say to Andy was not to go buying MAFs from stealers only to find the hesitation at 1800rpm is still there. I was merely suggesting that a remap could cure the problem, as it's what I've heard. I wasn't suggesting Andy goes out and gets his car remapped tomorrow. I was however suggesting that a remap is the best way to go when it comes to tuning, and that I've heard it *can* cure the issue.

Anyway. Bedtime.

[Rustynuts]

Yeah, OK. I just re read my post above, and it does read as though I was being snotty. Sorry, 'cos I wasn't. I remember from somewhere a case of someone with a Passat and a hesitation at 1800 rpm, but I can't find it now and I can't remember what the outcome was. I know it was a long chew which sort of terminated in the dealer saying it was normal, despite previously admitting there was a fault. Any one else remember this?

Sticky VNT mechanism maybe? Not quite returning to the proper position when coming off the pedal when changing gear. Slightly sticky N75 valve.

Does it hesitate at 1800 rpm all the time, or just once after you change gear (like if you hold 1800 rpm, is it a pig to drive).

[shark_90]

I was perhaps a little snotty as well mate, it wasn't meant I was a tired boy

It only hesitates at 1800 if the engine's at 1800 when you want power, ie you're crusing around 55, take foot off to regulate speed etc, slight power back on, and there it is. The engine does make a noise also, all I can liken it to is a "buzz."

From standing start/slightly lower revs it accelerates through 1800 without a dip or glitch whatsoever. I've heard the N75 valve also in the past, although that's further than my knowledge goes. I find it more an annoyance than a problem and so I haven't really worried about it until someone else has mentioned it again.

[andysills]

All,

Thanks for the info. I agree with Sharc, it is a slightly annoying problem, as in a bit of a niggle really. I have lived with it for 6 months but thought I might have a crack at fixing it. If it can't be resolved I'll happily live with it.

The 'sticky valve' idea mentioned does sound plausible since before posting, or even looking for help on the web, I imagined that the problem could be down to a valve or mechanism which was not moving smoothly (sticking).

Rustynuts - What is a VNT mechanism or an N75 valve ?

Sharc - I haven't noticed any noises associated with the 'hesitation' but it does come in at approximately 1800rpm (I had a test drive last night to check!).

Any more info that I can get on the possible sources of the problem (e.g. VNT mechanism and N75 valve) will be of help when talking to VW.

Cheers

Andy

[shark_90]

Andy - I think the noise is just a bit of diesel knock nothing serious, mine has done 122k! Still runs sweet as ever though

[asta]

Mine does it. Never thought much about it. I just assumed it to be a bit of turbo lag.

[Rustynuts]

N75 valve is a solenoid valve, which diverts vacuum to the turbo VNT actuator. The VNT (Variable Nozzle Turbine) actuator pulls and pushes a lever when vacuum is applied to it. The lever moves the variable vanes in the turbo to increase or decrease boost when required by the ECU.

ECU calls for maximum boost, N75 switches vacuum to the VNT actuator which moves the vanes to maximum attack on the turbo impellor.

ECU calls for no boost, N75 switches off vacuum to the VNT and spring returns the vanes to minimum position.

Anything sticking on either of these two functions will cause a mis match between boost required and boost provided. When a critical value is reached, the ECU will shut down the turbo actuator system (limp mode) until you switch off and restart.

[andysills]

postscript reply justto close this post. I took the car to another VW dealer for a service (heritage of salisbury). At the same time I asked them to look into the 'hesitancy' problem. They changed the MAF. Absolutely no change to the probelm whatsoever.

[njc021073]

I havea a Y plate 130PD estate, and it does exactly the same.

It has 133K on the clock and since I bought it a couple of years ago I have noticed a very little flat spot.

I mostly notice this as I am cruising at low revs on the Mway, and start to feather the throttle a little bit to slow down. Even though the throttle is still slightly pressed it suddenly goes of power.

I have never taken note of the revs, but it is probably around the 1800 mark.

The problem has not got any worse over the last 2 years, but is still definatley there. I was going to look into a new MFA at sometime, but might just leave it as it does not really harm.

[Durrsaku]

I have had that too with my A4, i don't think there is a problem with them. Although i did chang the MAF and i don't notice it so much now. Sometime you just have to take your mind away and not become obsessed with little things as such.

[vwsteve]

hi had same prob on my 130 sport check all your intercooler hoses carefully for leaks and splits especialy the turbo outlet s shaped one if the o rings are leaking on the top hoses replace them the noise you can hear is air escaping is it smoking alot when reved under load?

[JasXPear]

I've had this too on 2 different passats - seems to be the most common issue with the VAG Tdi130 that the dealers "dont know about". There's a big thread on the briskoda forum with the same issue on new Fabia VRs's. Mine's been into the dealers umpteen times to fix it replacing everything with no joy. Finally the dealer disconnected the EGR system and bingo bango problem solved. I asked if it would cause any issues/MOT emission problems and he said no. Been like that for the last year now, done 25k miles, got through an MOT, no probs at all.