Hi everyone, I'd be grateful for any thoughts on what might be causing the following issue please:

2012 A4 Avant TDI (143 bhp)

Every day, when I first start my car and accelerate away, the car judders really badly and struggles to accelerate - almost like its struggling to pull fuel through. But then after about 20-30 seconds of driving (max), the juddering stops, and the car then drives absolutely fine with no juddering or acceleration problems at all... If I drive the car again later in the day, it doesn't seem to do it - its just that first cold start of the day.

It's been doing it every day for the past 4 months, consistently on first start up (with the exception of just a couple of weeks recently when it stopped doing it, but now its back again).

The car fires up no problem on first turnover, and it idles really smooth on the driveway. The juddering is worse when the car's pulling uphill, but it does it downhill as well. It does it in all gears. I've tried idling the car for 10mins first after starting it before setting off, but it still does the judder. 

I've had it into my local independent vag specialist. They had the car for a couple of days, but couldn't replicate the issue, and found no fault codes showing. We couldnt fathom why it didnt do the juddering when they drove it, but did note one difference that they'd kept the car inside overnight (whereas I keep it on my drive). I'm not sure how that could be a factor.

The car's done 130k miles, gets serviced annually, and since the problem started, I've had the fuel and air filters replaced, and the egr valve checked (reported as operating correctly). I've run some injector cleaner through it, and switched to using premium diesel, but after 2500miles, the issues still there. It's not seemingly got any worse, but equally its not got any better...

I'm just not sure how to start troubleshooting it. Has anyone experienced something similar?

 

How does your clutch pedal feel?

I had something like that after I got a new clutch and flywheel. 

Ended up the clutch fluid was done along with the clutch slave cylinder. Very easy to fix.

Thanks for replying @848phantom

No noticeable difference with how the clutch pedal feels or operates. No sponginess or change in travel on it, and no issues with shifting gears. 🤷‍♂️

Can you get access to vcds anywhere?

Only thing I can think of is a failing tank pump and on hills it's struggling more to deliver the fuel?

 

Sadly haven't got access to vcds.

The vag specialist ran diagnostics on it for me, but advised there were no fault codes present 🤷

I would be looking at the tank pump...it won't show any alarms.

That or the map sensor 

MAP sensor looks to be relatively inexpensive (and easy) to replace - it might get that swopped out and see if it makes any difference.

Update on this @848phantom

I've swopped the MAP sensor out but sadly that's made no difference.

Interestingly though, the other morning I had the car idling on the drive for 10-12 minutes clearing the windscreen, and I when I set off there was no juddering.

So I'm wondering if it could be a sensor issue getting tangled up over engine/air temperature 🤔

Might it be worth me replacing the MAF sensor do you think? Might that have potentially to be causing the issue?

Engine mountings?? 

My 2 Pennie’s Worth is checking the heating element on the lamba sensors, can be checked with multimeter, they only heat briefly to bring the sensor into operational range so could match your 20-30 drive time. Ecu would be getting incorrect readings so would try to trim the fuel to compensate 

Thanks @Sid2020 - I'll have a look at that 👍

Thx @Magnet - I've read elsewhere that worn engine mountings can cause juddering. If they are worn though, would that cause juddering throughout the drive rather than just the first few seconds of acceleration 🤔

Possibly Jon, but worth an eliminating check. It’s always worth eliminating what you can.

Sticky brakes on one or more wheels??
Worth jacking up each wheel in turn first thing in the morning and checking each wheel for any significant drag. 
Prior to that, you could try leaving the handbrake off overnight to assess whether that makes any difference. 
Regards,

Gareth.

@Magnet - 100% with you eliminating as much as possible 👍

I'd wrongly assumed checking the mounts would be a crawl-under-the-car job, but a bit of googling's given me a couple of easy checks, so I'll definitely give the mounts a check over, as well as checking for sticky brakes as you suggest.

Cheers!

I have a worn engine mount. It rattles a bit then stops when warm but no juddering .

Need some to do a live scan first thing,

MAF sensor also can cause juddering but usually stays for the whole drive so it's more like something that's fixing itself once warm. Another check someone can do with vcds is your synchro angle on the cam sensor, could be out enough to cause cold shuddering and not trigger a MIL.

I got my belts done an the car wasn't pulling at all....then found my synchro angle was out , few mins with a couple of spanners and the car was pulling like a train again.