My car is poorly

arthurfuxake

arthurfuxake

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Ok, this is a strange one.

Car is as per sig. From a standing start all is ok, there is the slight delay and a bit of turbo lag until about 1200rpm as characteristic of this car but it's normal and has been like this since new. However, once on the move, all is not well. I can be pootling along in say 3rd, and when I give a bit of gas, it's like the engine has fallen asleep. The is no power and the revs slowly climb until about 3000rpm when all the torque and power slams in and the car rockets forward. Does this sound like a sticky EGR valve? The only way to get almost instant acceleration is by kick-down so that the revs are above 3000rpm. It feels like the turbo is not active below 3000rpm when is suddenly becomes full on. My car used to be very smooth, with a nice smooth build-up of power from about 1200rpm, but now the power is very aggresive and only from above 3000rpm. I only use shell v-power diesel btw. Any help would be most welcome.
 
Is it an intermittent fault or does it always do it?

It sounds like the vanes in the turbo could be sooted up, which is a fairly common issue. Or if it's intermittent possibly a MAF error, a scan should tell you more.
 
Well, it was serviced and the mechanic diagnosed a faulty MAF. He said the readings were well below spec so a new MAF was ordered and was fitted today. No difference! He said he'll have another look at it, but I'm not sure I trust him anymore. He quoted me £90 for the new MAF, then when I picked up the car they tried to charge me £156, so I had a good rant and eventually got them to agree to the original quoted price, but it wasn't without a fight. Anyone have any ideas? Is the turbo easy to get to? Is it easy to pull out so I can have a look at the vanes, or is it a pro job with pro prices?
 
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I'm starting to think this is ambient temperature related. Yesterday was the 1st day that it's been cooler (16degC) and the problem did not appear at all on my trip in to or out of work. This morning it was 15degC on the way into work, and there was no problem. It seems to be only when the air temperature is higher (maybe above 17/20degC). Is there any sensor that measures the temperature of the airflow into the engine? The MAF is brand-new so I'm discounting that. Does it measure air-flow as well as air-temp? The engine temperature guage has been behaving normally, so the engine isn't overheating. I had the MAF replaced on Wed last week, does it take a bit of time to recalibrate, or will the new MAF have an instant effect? I'm really stuck now, please help.
 
http://www.honestjohn.co.uk/forum/post/index.htm?t=42233 try this. I know it's not an A4 but it's a 2.5tdi passat. about 10 posts from the bottom the OP explains how he fixed his problem. He had the same symptoms as you (no power then a surge of power) and was also given an incorrect disgnosis of a faulty MAF - turns out it was some knackered solenoid that was causing the MAF to misbehave.

Might be worth a try?
 
Great find Nanafagis, thank you.

All was fine this morning, 15degc driving into work, turbo boosting normally.

Then on drive home, 24degc, problem raises it's head again!!? Not sure if the air temp affects the operation of the solenoid valves or not! I'm tempted to leave it as is and see how it drives over winter.
 
No problem, I just came across the same symptoms by doing a google search. I wonder if there's a way to check if the solenoid is faulty without taking it to a garage? I would hate for you to go and have it replaced just going on a link that somebody (me) on a forum posted and waste more of your money.
 
audi upgrades
my car does exactly the same as you are describing as soon as it is warm there is a hesitation then boosts normal. did a scan and a fault has come up with the air intake temperature sensor, just need to know where it is. Il open a thread to ask
 
Ok, I'm less convinced that it's ambient temperature related, but it's def intermittent. I've also noticed that there is a puff of smoke when the turbo does spool up and boost, but that might be because the revs are at 3000-3500rpm already when the turbo does eventually kick-in. Is there a solonoid valve that allows exhaust gas through the turbo, or is the exhaust gas permanently fed through the turbo?
 
the earlier v6 tdis had a vac solenoid mounted on the baulkhead on the o/s. this controlled the variable vanes on the turbo. short of an actuator test using diagnostics, i dunno how you test this at home.
 
Just popped into Awesome on the off-chance they could run a diagnostic. They've pulled the car in, no fault codes! Mech recons it's a duff MAF! He's gonna get a new one and pop it in, watch this space.
 
Well, new MAF fitted, no difference! Disconnect the MAF and the problem dissapears. Surely this 2nd new MAF isn't faulty as well!
 
Can't see any point in putting a 3rd MAF in, what are the chances of both new MAF's being faulty? They showed me the laptop which was displaying the requested air flow and the attained air flow. At idle, it was requesting 170ish, and attained was 170, so all fine. Increase the revs until the turbo boosts and the requested air goes over 700, but the supplied air is only around 200. The car isn't getting enough air(or dorsnt know rhat it is getting enough air)so is over-fueling and drowning itself. I've left it with them, god knows where to start, and how much it'll hurt my pocket.
 
Don't feel bad everyone, even the experts are stumped with this one. Everything is fine when the MAF is disconnected, but she runs like a dog even with several new MAF's. I can't see the dealership finding the fault if the vag specialists can't.

Anyone know the dangers of running with the MAF permanently disconnected?
 
Poor fuel consumption ? Did you check the actual socket where the MAF is connected ? I had an S2 before that occasionlly had fits with the MAF, turned out to be dirty contacts. Apparently it was known problem back in the day with the plugs working themselves lose and a mixture of poor contact and dirt causing problems.
 
Specialist rang today, he suspects the timing is out. Is it possible for modern ecu controlled cars to drift out of timing or is that only possible if the belt has jumped a tooth? If so, why is it ok when the MAF is unplugged? How do you check the timing, is it done through vag-com? I'm worried that the bill for this is increasing with every stab-in-the-dark they take!
 
I would guess he's talking about fuel pump timing rather engine timing? And if so then yes it can alter over time. Timing is done on vagcom yes, but I would have thought this was how they diagnosed the maf in the first place? If the maf controls the airflow, then I'm sure the fuel timing being out would be affected.
 
you come over to sheffield at all? book it in at du performance (where i work) 0114 2722020. id like a look at this!
 
Yeah, everybody wants a go at this, money for nothing, hours and hours of headscratching and guesswork at £50 odd per hour (excl VAT!). Gone are the days of getting results for ur money!
 
Murran, thanks for the offer, I'm a good few miles from sheffield, but if awesome don't diagnose it with their freelance specialist on Monday, I may just take u up on your offer. I'm running out of ideas now. What would happen if I ran the car with the MAF unplugged? It runs well with it unplugged, but will it do any damage?

PS. What's your hourly rate out of interest?
 
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Have you checked all the vacuum pipes?

When I had the engine re-build done on mine the garage kept delaying because they said there is a problem because its down on power. They thought it could be timing (camshafts) so took it all apart, double checked everything and then re-built it. Problem persisted. Next they checked fuel timing but that was ok too. Then the turbo was removed and checked, but that was ok too. Basically it came down to a small vacuum pipe near to and underneath the power steering resevoir that had split, pulled the split section out and replaced it, job done.
 
The car is still with Awesome, they have arranged for an expert to have a look at the car on Monday, but I'm assuming they have checked for leaking hoses or blockages?! I've already asked them to check the EGR solenoid valve as that has been highlighted as a possible cause. They are the experts, so I'm trusting them, I dont really want to tell them how to do their jobs, I'm not in the least bit technical.
 
think its £55 an hour at ours.
well, with cars as complicated as this and no fault codes to go on with, it becomes guesswork! depending on who you take it to, it meerly becomes educated experienced guesswork! lol.
 
So I've got the car back, it's not fixed. They had the car for about 10 days and they've spent over 15 hours on it. The great news is that they haven't charged me a penny! It's the 1st car in their 6 years that has defeated them. It's got another new MAF, the engine timing has been corrected, fuel pump timing checked, coolant thermostat replaced, it spent 4 hours on the rolling-road, every sensor reading checked, fuel pump pressures at each cylinder are perfect, and it all looks very healthy. Except it's not. They can see that it is over-fuelling at low rpm, but trhey cant see why. Jim had the ecu out and tested, he's checked the binaries and they look perfect, he's confirmed that it is the original ECU and it's never been remapped. He says it's almost like the ECU is forcing itself into "choke" mode as if the temperature is very low, but he's checked all temp sensor readings and they are ok. They say the only option now is to try a new ECU, and if they doesn't work, a new fuel pump. But at £800 for a new ECU, with no guarantee that it will fix the fault, and then another £800 for the fuel pump, and again no guarantee, it's looking grim. She ran like a real dog last night on my way home from work. On the plus side, she worked perfectly for most of the journey into work this morning.
 
Is there no possibility of borrowing another ECU?

The 2.5's are known for fuel pump problems aren't they.
 
Finding someone willing to provide an ECU for testing purposes is almost impossible. As with any elctronics, once it's been plugged in, who knows what's happened to it. I wouldn't feel comfortable putting someone else's working ECU into my faulty car, there is a possibility that whatever caused mine to go faulty in the 1st place will cause the borrowed ECU to fail too.

I would have thought that a faulty fuel pump would cause fuel starvation rather than overfueling? Also, the fuel pressure readings were perfect for each cylinder, I would have thought a faulty pump would show wrong pressure readings?

I'm afraid to drive her now, it was embarassing trying to pull away from lights last night, it took ages to reach 2800 rpm where the power finally kicks in.
 
Hmm it's not really an answer is it, but I don't know what else to suggest.
 
with the maf unplugged the ecu can see its open circuit so it subtitutes a known safe value.... if it runs much better with it unplugged then youve got to start there. have they checked voltages and resistances of the maf wires back to the ecu? resistance and so a voltage drop somewhere?
 
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Would it be a big job to replace the wiring loom from the MAF to the ECU? Where does the ecu live on the 2.5TDi? If it's in the engine bay, could be an easy job?
 
The ECU is on the offside of the engine bay under the black cover (shown removed here)

12.jpg
 
dont think you need to change the loom just find the defective wire start with belling them out then go to checking the resistance but un plug the ecu first.
 
I've had an engine light on for a while.
It was disgnosed at the inlet manifold flap by Audi, have been meaning to get it fixed but it was giving no symptoms for 6 months.

Recently, I have had the same symptoms described in this thread. An independent specialist has said there is no signal at inlet manifold flap, and said it could be that or the wiring, and if that doesnt fix the prob, it could be anything but suggested the fuel pump be next thing to look at.

The timing belt was done at 73k it is now on 119k - the are supposed to last 60k? Im wondering if i should get that done early too.

Did you get to the bottom of your problem in the end?
 
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