How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Matt Your Own Question
Matt, Engineer
Category: Audi
Satisfied Customers: 21990
Experience:  Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
Type Your Audi Question Here...
Matt is online now
A new question is answered every 9 seconds

2004 Audi A3: dsg with 90k miles..test drive..parked around the back

Resolved Question:

Hi there, I now live in the UK and about 2 weeks ago I privately purchased a 2004 Audi A3 3.2 Quattro DSG with 90k miles on the clock. I took the car for a test drive before purchase and it ran very well, was also in very good original condition. It was delivered to me on a transporter and parked around the back as I had no other way to collect it. Later that day I took it out for a run and within minutes it started misfiring very badly under load but would idle OK. I got the RAC to look at it and they said the ECU was reporting multiple misfires on all 6 cylinders and that a garage would need to look at it. They also advised that it was strange that the engine light was not on. I got the car transported to the nearest garage they recommended which was in Ealing. After looking at it they advised that 2 pencil coils were faulty and recommended replacing them all which was done. 500.00 pounds later I collected the car and the problem was gone although I did notice a small miss when idling which was very slight and more like a small flutter than a solid miss but it did show up as a flat spot between idle and about 1200RPM when taking off. Also when idling if you very lightly increase the engine speed between idle and 1200RPM the engine will die off and start hunting a bit and once you get above 1200RPM it will rev off and is fine. Firstly it seems very strange that it drove OK a couple of days before on my test drive as I would have definitely noticed the missing problem as it was very bad and almost seemed to be misfiring on all cylinders and not just two. It is also strange how these two coils could have failed in just a few days and on the back of a transporter, also that the ECU showed the problem on all 6 cylinders, which is what it felt like, but the engine light was not on?

On that weekend the next day after collecting it we shifted from Ealing, London to High Wycombe and drove the car to and from London and High Wycombe several times and around High Wycombe without a problem apart from the idle miss and flat spot up to 1200RPM. However on the Monday night the engine light came on but apart from that it ran fine until the Friday morning where after driving about 5 minutes into work the car started missing again very badly lake before except it was now at the lower revs up to about 2000RPM and would not idle at all unless you worked the accelerator to keep it running. Again it seemed like it was misfiring randomly on all cylinders and whilst it could be an ignition fault it seemed more like it was starving for fuel as when you worked the accelerator you could get it to pick up and run a bit all be it very roughly and totally un-drivable. Also it would run over 2000RPM plus all 6 pencil coils had just been replaced. I arranged to take it down to a local VW/Audi garage and when I got into the car it started and drive down there fine with no sign of the problem apart from the low speed/take off flat spot. The garage checked the ECU and advised that it had misfiring listed on 3 cylinders and told me I needed to change the 6 pencil coils, which I had told them had been changed just the week before. They told me I should take it back to for first garage otherwise I would need to pay them another 400-500 pounds to get the coils changed again, which is not easy now I live and work in High Wycombe and the other garage is in Ealing London. I drove the car from the garage back to work a couple of minutes down the road and it was fine but on the way home a couple of hours later I stopped to get fuel and the problem started again at the service station. I managed to get the fuel and get the car off the forecourt to the side where I sat starting and stopping it for about 20 minutes. It would start fine every time and after a few minutes or less it would start misfiring badly but interestingly the more time went by the longer it would run for each time until it got to the point where it was fine again and I could drive it home without a problem apart from the idle and flat spot. I Haven’t tried it again since then but will do when I get a chance when it had stopped raining here. I will obviously need to get someone to look at it but was looking for some guidance on what may be wrong as I do not know anyone here that I have experience with to look at it and do not have much faith in a lot of garages and dealers as I have heard a lot of horror stories and experienced a few problems before with garages and dealers who really don’t know what they are doing and just keep replacing parts until they find the problem and then hand you a huge bill as this is the only way they know how to fix things. I have done quite a lot of mechanical work myself with rebuilding engines and gearboxes etc but that was on simple carburettor type engines and nothing like this 3.2 V6 but I do at least have a few clues know that the garage’s idea of replacing all 6 pencil coils in less than 10 days is maybe not where the problem lies? With my limited knowledge it now seems more like a fueling problem where there is an issue with the sensors or ECU and it is not operating the fuel injection properly starving the engine. It also seems like there are two problems being the idling/flat spot and the bad missing problem but strange that none of them were present when I test drove it a few days earlier? I also wonder if there could be a problem with the fuel getting low as the fuel light was on when it was delivered and had the original under lead missing problem and the fuel light went on, on the Friday morning when it started missing again but then it ran OK later that day to the garage to be looked at and the fuel was still low. The fuel was also low when I drove it from the first garage who changed the pencil coils until I got to a service station and it ran fine then also.

Sorry this is so long but I thought it best to explain everything as best I could and hopefully someone there can give me some pointers as this could cost me a fortune if I am not very careful or lucky. Would also be good to get some good pointers for service people in my area if anyone there can help? I look forward to hearing back, cheers, Gavin

Submitted: 5 years ago.
Category: Audi
Expert:  Matt replied 5 years ago.
Hello Gavin

I'd agree that it sounds like a fuelling issue This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.
As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.
if the engine condition is the same then chances are the meter or the connection to it is faulty

Air leaks are very temperature dependent as gaps can open or close up as things expand with heat, so the weather and engine temperature can effect them.

This leads them to be quite intermittent in the case of mild leaks

its also worth cleaning the airflow meter by removing it from the car and spraying the exposed sensor wires inside the tube with a brake or switch cleaner - ensure that the cleaner is one of the old fashioned, non Eco type that does not leave a residue

On no account touch the sensor wires with anything physical as they are extremely fragile

as for an Audi specialist try:

Customer: replied 5 years ago.
Hi Matt, thanks for your help and I had not thought of an air leak which would fit the idle miss and flat spot as it feels a bit like that or a timing issue. But not sure about it being the problem for the major missing problem as it is very violent and seems to come and go so not just there a bit and gets worse, more like one minute its running and the next the engine is trying to climb out the engine bay. Also I would expect it to get worse with higher revs but having said that I have no experience with ECU controlled engines and that could be causing something completely unexpected to me. If the weather is clear enough tomorrow I will check for air leaks as suggested and check out the air sensor, will also try removing the sensor connection to see if it replicates the problem, in fact I may try that first. Unfortunately having just moved to the UK I do not have much gear to do much and it may also take a bit to track this down so will probably need a bit more help on this as I try and sort it out if that is OK but I will accept your answer in the meantime so you at least get paid for your help which is appreciated. One other related thing to the idle miss/flat spot is that I have read a bit about stretched timing chains in these models which sounds like a bit of a nightmare and would possible cause this type of problem so in your experience how common is this? cheers XXXXX XXXXX Gavin
Expert:  Matt replied 5 years ago.

Thanks for the extra information

If the misfire is that violent then yes a simple airleak would have to be pretty major to give this severe an effect - but its also possible the MAF meter is faulty

Its still worth measuring fuel pressure as I mentioned as this would also give a misfires and a flat spot as you describe

as for the possibility of a stretched chain then yes this can happen and its not something that a diagnostic will show up so the engine needs partial dismantling to determine if the chain has stretched
Customer: replied 5 years ago.
hi Matt, thanks for that and I will try disconnecting the air flow meter to see if it makes the car show the fault. I also understand that there are some Co sensors in the exhaust that provide data for the ECU to set the fuel mixture/injection rates so could they possible be faulty? Having said that there would be one for each cylinder half of 3 pistons and I suppose it would be unlikely both fail at the same time, each time to cause all 6 cylinders to misfire at the same time? I will need to take it to a garage to get the fuel pressures etc tested so any other clues in the area would be helpful and I will take it to Dashwoods as suggested as hey seem like an honest bunch according to their testimonials.

OK I hope there is nothing wrong with the timing chain at that sounds very expensive to fix so is it a common thing on these engins, have you come across many with this problem.

Haven't accepted the answers yet as I'm not sure how to find the post if I need a bit more info perhaps after looking at the car and taking it to Dashwood's if it doesn't get sorted so please let me know how to find this post and get hold of you so I can accept your answers and pay you. Cheers, Gavin

Expert:  Matt replied 5 years ago.
Hello Gavin

You're right there are a pair of O2 sensors in the exhaust and yes these do effect the fuelling as the ECU uses these to correct minor fuelling issues

if a sensor is faulty then this can produce over and under fuelling do its worth disconnecting the sensors one at a time to force the ECU to discount the sensor output

there's no official recall for the timing chain issue but there are enough reports to make it common knowledge that its an issue with this engine - having a regular oil changes every 6K miles does seem to help however

if you press accept I can still continue the conversation on this post
Matt and other Audi Specialists are ready to help you