Audi A3 170 TDI Fault! Need advice!

[Harry Kendal]

So last month I bought an Audi A3 2.0 TDI 170 56 Plate. The car ran great when viewing and when taking her home etc. However the next morning when I came to start it, it just cranked and cranked for about 10 seconds, as if it was hunting for fuel, eventually it fired up then died. So I tried to fire her up again and about 5 seconds later it fired, I revved her a couple of times and then she was okay ( I use the term 'okay' loosely as she was juddering for the next 15/20 seconds or so, not majorly, but enough to feel it). Anyway, on the next journey later that day it was fine, fired up first time no problems what so ever.

Now this has been the case for the car now since buying it. I've tried contacting the guy but nothing, obviously dodging me, but I'm not willing to give up on her. I'm avoiding taking it to a specialist because moneys tight at the moment so I've been attempting to repair her since day dot.

I changed the coolant temp. sensor last week and it seemed to cure it for about 2 days, but then it came back, so I replaced the sensor again thinking I had a dodgey sensor, but nothing, back to normal... I've serviced it (Fuel filter, Oil filter & Oil change, Air filter). Now for me this is the strange part, i't runs great once hot, its only the first start of the day no matter whether thats at 7am or 3pm. Outside temp doesn't seem to affect it, it simply seems like its first start is poop. It also tends to chuck out a fair amount of white smoke every now and again, mostly at cold starts, but sometimes when warm.

I have noticed a couple of times when its on its first start of the day, if I boot it a little in 2nd it somewhat struggles to climb up the revs, it feels as though it drops its ar*e for a second every 1000 revs or so, but this isn't consistent. I've had a mate with a snap-on reader scan the car and no codes have come up, so I'm just stabbing in the dark here.

I've just ordered a MAF sensor off eBay thinking its potentially worth a shot, I noticed the MAF's already been changed before to an aftermarket one so figured that could be out.

Any suggestions would be appreciated, I'm not majorly skilled with cars but willing to give most things a shot.

Thanks in advance!


Side note: Whilst changing the coolant temp. sensor, I found a little steel box under the air filter housing that was plugged in and loosely hanging, it had just enough of a label left to see that it is some sort of performance chip -_- I can't make out a brand of it so I can't even research it. Without posting photos of this, does anybody technical minded know if I can simply unplug this, as I have no idea what it is doing, or does it need to be somewhat re-programmed in order to remove it. From what I can tell it looks as though its been hard wired into the loom somewhere but cannot trace wires without stripping front end completely down.

What a nightmare this cars turned out to be.

 

[Daveyonthemove]

It sounds a bit like fuel starvation.
I'd look for fuel leaks, injector condition, fuel filter condition etc.

you should be able to remove the tuning box, it will sit between the wiring loom and the sensor it's connected to, so unplug the box and plug the loose wire into the sensor the box was plugged into and that should put the car back to standard.

 

[Rideen]

I would start by removing the dodgy box first (don't forget to reconnect the original cables back where they're supposed to go).

PD170 should have DPF fitted and if hasn't been removed before tuning box has been installed it can get really bad for the DPF (more fuel = more soot = DPF clogs faster).

 

[aqibi2000]

Upload a photo of the timing belt tensioner (so can see the arrow) as this can cause poor starting without throwing camshaft error. It'd say fuel related too

 

[SootySport]

Get rid of the tuning box for starters.
With cold starting problems the glow plugs will always be a suspect if the car runs perfectly when hot.
You could end up blindly spending money on parts without curing the problem and maybe best off seeing a
VAG diesel expert for a diagnosis.
What’s the mileage on the car?

 

[Rideen]

You can also try VCDS map section and see if there's a forum member nearby to scan your car for faults.

 

[Genius]

OK so it's a while since I driven a diesel so not sure if this is even a thing and if it is it's probably obvious... But may as well ask in case it is something you didn't realise...

Are you waiting for the glow plugs heat up before turning the ignition to start it?

Even if you are like sootysport said could it be worth checking they are working correctly? Thinking a diesel not starting cold but then fine when warmed up maybe a glow plug issue, I'm not a mechanic so my advice definitely should be taken with a pinch of salt but should be reasonably cheap to check?

 

[Rideen]

You usually wait for the glow plug light to go away and then start. Not sure if 8P FL does it by itself, but on 8V, you flick a key, it preheats the cylinders and when the glowplug light is gone the starter kicks in.

As many suggested before, remove the box first and do a VCDS scan of the car. It might be able to tell you A LOT.

 

[Harry Kendal]

Thanks for the speedy replies people I’m currently at work but as soon as I get home I’ll be taking pictures of this box and posting on here seeing if anyone can point me in the right direction. Not too clued up on performance boxes etc and not a clue how it’s wired up to the car, not sure if it’s had extra connectors put in place to make it work or whether it’s a simple pass through box. But I’ll defiantly be removing that ASAP because I have no idea what it does (apart from supposedly increase performance), and have no idea what it’s doing to the car
I’ll report back later

 

[Harry Kendal]

OK so it's a while since I driven a diesel so not sure if this is even a thing and if it is it's probably obvious... But may as well ask in case it is something you didn't realise...

Are you waiting for the glow plugs heat up before turning the ignition to start it?

Even if you are like sootysport said could it be worth checking they are working correctly? Thinking a diesel not starting cold but then fine when warmed up maybe a glow plug issue, I'm not a mechanic so my advice definitely should be taken with a pinch of salt but should be reasonably cheap to check?

Yeah I’ll always wait for the glow plug light to go out, I’ve even tried cycling the ignition to warm them several times. Doesn’t make the slightest difference

 

[ch1z64]

Totally agree with the members above , but to save yourself a lot off grief and in the long run money ( unless you find a miracle cure ) i would go by what @SootySport said Vag Diesel specialist and take it from there thats why there called Specialists

 

[Daveyonthemove]

When you do get it started, take the engine cover off and look for any diesel escaping the injectors.
Cold start problems shouldn't be a glow plug problem during warmer months, they don't really need them until it gets much colder.
I think it sounds like it struggles to start due to fuel starvation, and when it finally gets the fuel it runs ok. After the car has been left the fuel pressure drops and the car struggles again.
I would check the fuel pump and look for air entering the system through a leak somewhere.

 

[Harry Kendal]

Turns out that box isn’t a performance chip, after a bit of investigating it’s actually for the xenons on 1 side, pretty deceiving as on the box it’s got half a label and the bit that’s still there says “performance” ... I unplugged the MAF sensor and it started somewhat better, it didn’t die this time. It hesitated a bit and was a rough start but didn’t die. Would this indicate a malfunctioning sensor despite no codes?
I also noticed that with it plugged in and revving I had a fair amount of white smoke out the exhaust, with it unplugged and revving, the white smoke was reduced...

The new sensor comes tomorrow so will report back once changed, if this isn’t it I’ll have a little look for air leaks in the fuel line but as mentioned originally I’m not completely companant on repairs so odds are it’ll go in to a specialist

 

[JimS3]

This won’t be glow plugs, these engines start fine in warm temperatures even with 4 dead plugs.

There are many things that could cause these issues and I would recomend taking it to a VAG specialist to save yourself much frustration.

Your engine has a known problem with dodgy injectors that can cause the issues you describe, it was however a recall and you should check if yours had the injectors replaced. If not you may still be able to get this done.

If you do want to persevere yourself, here’s a few things to check.

The ECU needs to see a certain engine crank speed before it will add fuel, so a weak battery or bad starter motor can cause slow starting.

Could be a failed lift pump in the fuel tank, or faulty tandem pump or a leak alowing fuel to drain from the pipes to the tank. You can check this by replacing a section of the fuel hose with some clear hose and check for bubbles.

Also worth checking the timing, easiest with VCDS software, it’s the Torsion value you need to check. Anything higher than 3 either minus or plus can cause starting issues.

A garage / individual who knows what they are doing with VCDS software could check all this for you.

Do suspect injectors and check recall as most likely issue though.

 

[Harry Kendal]

This won’t be glow plugs, these engines start fine in warm temperatures even with 4 dead plugs.

There are many things that could cause these issues and I would recomend taking it to a VAG specialist to save yourself much frustration.

Your engine has a known problem with dodgy injectors that can cause the issues you describe, it was however a recall and you should check if yours had the injectors replaced. If not you may still be able to get this done.

If you do want to persevere yourself, here’s a few things to check.

The ECU needs to see a certain engine crank speed before it will add fuel, so a weak battery or bad starter motor can cause slow starting.

Could be a failed lift pump in the fuel tank, or faulty tandem pump or a leak alowing fuel to drain from the pipes to the tank. You can check this by replacing a section of the fuel hose with some clear hose and check for bubbles.

Also worth checking the timing, easiest with VCDS software, it’s the Torsion value you need to check. Anything higher than 3 either minus or plus can cause starting issues.

A garage / individual who knows what they are doing with VCDS software could check all this for you.

Do suspect injectors and check recall as most likely issue though.

Injectors have already been done on recall, may try and change fuel pipe soon, but even so I wouldn’t have a clue how to fix it there was an air leak thanks for the reply Jim

 

[aqibi2000]

Injectors have already been done on recall, may try and change fuel pipe soon, but even so I wouldn’t have a clue how to fix it there was an air leak thanks for the reply Jim

The air leak if found would usually be caused by the fuel filter housing cobimed with poor installation technique.

 

[Rideen]

White smoke is usually a sign of engine running too lean or burning coolant.

Is the car losing any coolant? Coolant in cylinders would also cause these simptoms (apart from faulty injectors and/or fuel pump), if you're lucky enough, it'll only be a cylinder head gasket replacement.

 

[Harry Kendal]

White smoke is usually a sign of engine running too lean or burning coolant.

Is the car losing any coolant? Coolant in cylinders would also cause these simptoms (apart from faulty injectors and/or fuel pump), if you're lucky enough, it'll only be a cylinder head gasket replacement.

It doesn’t seem like I’m loosing coolant, would it be noticibly going down if that was the case? Or would it only be little bits? Since I’ve changed the coolant sensor twice I’ve topped up the coolant twice in 2 weeks but that’s because I had lost some whilst changing the sensor. So at the moment it’s been hard to check coolant loss with me topping up.

 

[Rideen]

It doesn’t seem like I’m loosing coolant, would it be noticibly going down if that was the case? Or would it only be little bits? Since I’ve changed the coolant sensor twice I’ve topped up the coolant twice in 2 weeks but that’s because I had lost some whilst changing the sensor. So at the moment it’s been hard to check coolant loss with me topping up.

It might or might not be easily detectable. You should see some decrease of the amount of fluid after 500 miles or so though, and it is easier to notice if the car has been driven at operating temperature because the coolant will be under pressure and will disappear faster than if the car was cold.

This might be a long shot, but it is the least painful problem (it hurts less than new injector(s)).

 

[Harry Kendal]

It might or might not be easily detectable. You should see some decrease of the amount of fluid after 500 miles or so though, and it is easier to notice if the car has been driven at operating temperature because the coolant will be under pressure and will disappear faster than if the car was cold.

This might be a long shot, but it is the least painful problem (it hurts less than new injector(s)).

If it were a coolant leak would the smoke not be visible practically non stop? Because it’s sort of an on and off thing, usually when cold but rarely when hot

 

[Daveyonthemove]

White smoke normally indicates an injector issue or coolant being consumed by the engine.
I would expect it to be an injector/fueling problem as it struggles to start.
This link might help: https://costeffective.com.au/2017/03/05/diesel-smoke-tells-you-a-story/

 

[ch1z64]

Now putting your hand in pocket and buying a Haynes Manual could help you understand your engine and help you do some small maintance on it , but as advised buy a few members taken it too a Vag Diesel specialists is going to be the only true way to find out whats wrong with your car, and then hopefully you will have a conculsion .

 

[Rideen]

If it were a coolant leak would the smoke not be visible practically non stop? Because it’s sort of an on and off thing, usually when cold but rarely when hot

If it's leaking into the cylinder, it would fill the cylinder with some coolant when the engine is off thus making it hard to start and cause white smoke when cold (due to the burning of the remaining coolant). When engine gets warm the white smoke disappears because the leak is very small.

Get injector correction values tested by the way.

 

[Harry Kendal]

Update ——

Replaced MAF sensor for an eBay one, not much difference.
Also repaired a Boost leak under the car where oil was all around the seal ( see photo ). And added some fuel cleaner to the system.
All I can say now is it’s still doing the same things but somewhat worse, I want to put it down to the cleaner in the fuel making it run a little lumpy but cannot say 100%.

One of my close mates just bought a 2010 A4 2.0 TDI and his is doing the same, took it into the garage and he reckons it’s probably an injector seal. So after this cleaners run through the system I’ll see for a difference but if nothing then I’ll be taking it in.

It’s now idling a little rough at first start (cold), really is hunting. It’s stuttering a little and does judder, but as mentioned I can’t decide whether that’s the cleaner or just getting worse. Either way I can now say I’ve done as much as I can without being a pefessional to try and resolve the issue. Will post more updates for anyone else with the same issue in the future.

Thanks for your help people and I really do appreciate the replies.

 

[Harry Kendal]

There was the bottom boost pipe leading from the intercooler.

 

[Harry Kendal]

Update #2
Started the car today, first start, and it started fine,
No hesitation, didn’t stall, didn’t seem like it was going to stall.
So, question, because of the boost leak, is it possible that because it’s now fixed and I ran the car yesterday, it’s now built up air pressure and will start okay?

 

[Daveyonthemove]

Unlikely, Boost doesn't stay in the system when it's not in use, and it would build up very quickly anyway (1-2 seconds).

 

[aqibi2000]

You can get oil tested for diesel contamination which would come through injector seals (although there is always a bit of leakage expected)