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Delinquent

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My 2.4SE auto developed a problem at the weekend, and I'm at a bit of a loss where to start while I wait for the diagnostic tool to arrive...

Basically on Saturday it started to develop a bit of a cough, nothing major, then at a junction at idle the revs suddenly dropped before resuming normal service. Nothing major and no warnings given.

Wife took the car out Sunday and it stalled several times on her at rather inconvenient moments (on pull away) but I couldn't reproduce on the drive. Later in the day, it conked out on me completely and the "INSP" warning started flashing on the computer, got it going and home after which it sat and idled beautifully for 15 minutes at a time, then suddenly either drop revs and have a lumpy idle for 2-3 seconds, or it'll cut dead, as though the ignition has been switched off. After lumpy / cut off and restart it'll again run beautifully till some random moment it'll have another paddy.

About the only thing I have noticed so far is that there is a high pitched hum that I think is coming from the throttle body - is this normal?

Any thoughts?!
 
audi upgrades
if you have a vagcom do a scan, you can also try a Throttle body aligment.

by your description it looks like the throttle body sensor. but first try a vag scan and alignment.
 
N80, i bet if you open the tank cap when its spluttering it will clear out. The insp light is a coincedence, it is reminding you a service is due thats all
 
I don't have a vagcom specific, but I have access to a "generic" one which I'm assured will read it - only problem is it's in the owners car on holiday! Desperately need the car before they are back so was looking to "fiddle" in the mean time. I've not done a TBA before, will have a read up on it in a mo!

Wouldn't the coil packs give more of a miss on some cylinders than a dead stop / low idle?
 
TB aligns itself afaik if you leave the ignition on and dont start the engine for three minutes or so

The high pitched noise from the TB area also happens on my brothers S4, we noticed it after changing the control board in the Throttle body but the car runs perfectly now so we can only assume its normal!
 
aragorn, I'll give that a go later, just in case! Good to hear that someone else has the high pitched noise, it's one of those things that if you know it's common you can ignore, if you don't, you wonder if you're wasting time looking anywhere else! Think I may just have to fork out for a vagcom though, which is mildly annoying as it's more than I paid for the car (suppose that'll be a bit of karma pay back for being a jammie git with the purchase)
 
I would say coolent sensor just starting to play up, mine did this but it could even be the crank sensor but I would go with the coolent sensor first plus it's a cheap and easy fix.
 
didn't realise it had a free version - that'll do the job then :D cheers
 
well, got the diagnostics report in....

no error codes found. How very helpful!:uhm:

It did however cut out 3 times in a 1 mile trip...
 
if a sensor is giving a false reading it may not show up on a scan as it may still be running within tollerance.
I'd probably look at the air mass meter considering how prone they are to playing up.
 
Well had it apart again tonight. Cleaned out the MAF and put a new coolant sensor in as a bit more manual diagnosis showed the problem only exists when the car is fully up to temp. Running the car for 15 minutes afterwards showed the problem is still there, but also highlighted the fact that it must be running SERIOUSLY rich - going by the huge amount of soot on the floor below the exhaust!

Interestingly - the temp guage in the car appears to still be intermittent (unless with the outside temp. at 10 deg while running at... erm... quite high speed on the motorway the coolant temp could really be less than 60 deg?!)

I'm wondering if it is related to the wiring between the coolant temp sensor and the ECU - or maybe a common earth between sensor ECU and guage? Anyone have a wiring diagram they could check for me and see if there is a common earth or other likely place for the electrickery to spill out on the floor?!
 
my 2.8q started playing up just after i got it where it was stalling and had the revs dropping in traffic. turned out to be a broken plastic breather under the engine cover on the near side. previous owner had repaired it with some electrical tape. I put some heat shrink round it and then everything was fine. could it have the same brittle breather on the 2.4?
 
dsmclark30v said:
my 2.8q started playing up just after i got it where it was stalling and had the revs dropping in traffic. turned out to be a broken plastic breather under the engine cover on the near side. previous owner had repaired it with some electrical tape. I put some heat shrink round it and then everything was fine. could it have the same brittle breather on the 2.4?
Click to expand...

Not sure if it's the same one as you had, but we replaced about 8 vacuum tubes that were all brittle and on the way out as a first port of call. These were at the back of the engine under the plastic cover - will have another poke around and see if we've missed any just in case, but its the temperature gauge that's got me thinking, as the sender unit is brand new for that not to be working I think I've got wiring issues - although I'd have expected this to give a fault code which it hasn't!
 
Delinquent said:
Not sure if it's the same one as you had, but we replaced about 8 vacuum tubes that were all brittle and on the way out as a first port of call. These were at the back of the engine under the plastic cover - will have another poke around and see if we've missed any just in case, but its the temperature gauge that's got me thinking, as the sender unit is brand new for that not to be working I think I've got wiring issues - although I'd have expected this to give a fault code which it hasn't!
Click to expand...

http://www.audiworld.com/tech/eng.html this is the one i had to repair. but might be different on the 2.4
 
fault code would only appear if the signal went out of range...

if its within range, but incorrect, then it'll happily run badly thinking its at 60c when its at 90

Can i just check something, your not leaving the car idling each time you "test" it are you? its really not good for the engine to leave it idling for long periods of time...

i'd run the engine up to temp and compare the reading in vagcom as a starting point. The other option might be a sticking thermostat. But if the engines fully up to temperature and the guage is reading 60c then you need to find out wether its the sensor/wiring or the guage before you go any further.
 
Thanks, I think it's the same actually! Going on how brittle other parts have become, it wouldn't surprise me in the slightest if that was gone too so well worth a poke about later. I also found mention on that site about cleaning the throttle plate to cure lumpy / erratic idle so may give that a go.

One thing I was quite pleased about last night - I'd heard horror stories about changing the coolant sender unit, needing to take off the ducting from the throttle body which in itself is a PITA - I found that by taking the top off the air filter (30 second job) and unhooking 2 coolant pipes off the top, I could get my hand down the resulting gap and access it quite easily - took about 5 minutes total!
 
aragorn said:
fault code would only appear if the signal went out of range...

if its within range, but incorrect, then it'll happily run badly thinking its at 60c when its at 90

Can i just check something, your not leaving the car idling each time you "test" it are you? its really not good for the engine to leave it idling for long periods of time...

i'd run the engine up to temp and compare the reading in vagcom as a starting point. The other option might be a sticking thermostat. But if the engines fully up to temperature and the guage is reading 60c then you need to find out wether its the sensor/wiring or the guage before you go any further.
Click to expand...

Accept what you are saying about values, but wouldn't the resultant misfire have create a code of it's own?

LOL yeah I am leaving it idling. I know all the theories behind it (used to be a mechanic back when cars were mostly nuts and bolts rather than 15 computers with some pistons welded on....) but I think the car has far bigger problems at the moment! (like the possibility that if I can't sort this in the next couple of weeks I'll be breaking it for spares...)

Unfortunately vagcom is back off the list at the moment as the laptop has died permanently and replacement is not an option, but given the fact that a brand new sensor yielded no change in behaviour whatsoever I'm reasonably confident we can scratch that off the list for the time being. What is most annoying is the intermittent nature of the fault - running absolutely spot on for a bit, then a couple of minutes of hesitating / stalling, then running absolutely fine again.
 
Going back to the posts about sensors/wiring...

I agree that in some instances, sensors can report incorrect values but still be within normal limits, and therefore not throw an error - so that's a possibility. It's not the same for all systems though, because if there are secondary or tertiary sensing elements on the same system and one doesn't tally with the other(s), you tend to get an Implausible signal DTC. I'd be tempted to suspend investigation of this for the moment though, because if you've changed the Coolant Temperature Sender it's relatively safe to say that's OK; and I wouldn't worry too much about the gauge until you've checked other things out, because once they get to a certain age it appears that VAG temperature (and fuel) guages are quite prone to neurological disorders - they think what they like, and it's not necessarily fact...

As for serious electrical shorts - things can throw up Disconnected/Short to Positive/Short to Ground DTCs if there are wiring faults, so I'd be putting that a little further down my list of suspects for now too...

Have a look at the other suggestions folks have made, then fall back to the two above once you've ruled the rest out I'd say...

Regards,

Rob.
 
Delinquent said:
Accept what you are saying about values, but wouldn't the resultant misfire have create a code of it's own?
Click to expand...

Yes, normally a 'proper' misfire, caused by ignition components will generally throw a DTC noting which cylinder(s).

Regards,

Rob.
 
All fair points Rob - I'll start with a new MAF sensor and cleaning the throttle body then work my way down the list I think! It'll have a max of £250 spent on it before it's broken for spares, so lets hope it's not something too far down the list...
 
Sounds like a plan, but I can't help thinking I'd also check (unless you have already of course) Byzan_A4's N80 suggestion and dsmclark30v's broken breather theory before you go buying a MAF, as at the end of the day they're both cheaper to check (you don't have buy a new bit to find out the one you've got works). If you're thinking about the MAF, you might even consider running the motor with the MAF disconnected - it's not the best situation, and it'll give you a CEL; but if that's causing a fault it should at least run steadily without it connected. You could of course clean the TB before replacing too. I'd give it a good inspection and manual operation test (pull and push at the pully and pushy bits to see if they stick at all) and it it's filthy and/or sticking, give it a good clean. I don't know what the 'recommened' cleaning agent is - but I used brake cleaner once and it did a great job - just make sure it's all gone before you put it back on the car...

Regards,

Rob.
 
Sorry forgot to say I checked the breather just after I posted that other bits in there were brittle - it's fine.

Must admit completely forgot about Byzans suggestion :redface: - I'll try whipping the cap off later, where is the N80 located?
 
on my 1.8T its mounted above the airbox, has some vac pipes and a electrical connection on it

I wonder if the problem could be related to the ingition amps? They get hot and stop sparking correctly...
 
Cheers Aragorn - We've replaced a shed load of vac pipes in the engine bay as they were all breaking up, I wonder if some of the rubber got down inside the unit! Have a good list of things to check over the weekend (no tinker time for next couple of days) so fingers crossed n all that.
 
Had another poke around at the weekend, went through everything left on the list - the throttle butterfly was a bit of a mess so cleaned that up. Handy hint if you want good visibility when cleaning this, forget a mechanics mirror, get a learner driver rear view mirror with a suction cup fitting, wipe a bit of the bulkhead and stick it on! No guess work. Checked all the breather hoses, Purge valve etc etc, and eventually came back to the MAF sensor. Disconnected it and after a bit of a bitch to start, it ran far better! To confirm it we checked the resistance of the MAF sensor by sticking pins in the leads - a fraction of a second before the idle went rough, or dipped, the resistance from one of the pairs of pins became very irratic, and just before it stalled it went open circuit. Hopefully that's fairly conclusive evidence, so will be purchasing a new one today.
 
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