dealer recognises misfire but no codes

[mof777]

hi guys

apologies if were going over old ground here.

heres the symptoms

the car starts fine but driving it for the first mile is really bad - it hiccups badly and your passengers even know it

2nd 3rd 4th all the same. once warmed it seems fine although i feel the problem may still be there but very slightly

its been to dealer and theres no codes whatsoever - they are leaning towards spark plugs.

so is it possible for a bad plug not to throw a code??
they also say there is no update software available but refrained to tell me what version im on

any advice appreciated

[WillRS]

I had / have this - was worse when cold i.e when outside temperature was cold. was really noticeable and made you feel like you couldn't drive properly !

I had the spark plugs changed - made no difference

the only thing which seemed to make any difference (and I didn't get it done for this reason!) was the full MRC carbon clean.

the cold idling whilst not perfect was a HUGE amount better...

since the weather has been warm(er) the problem doesn't seem to happen as much if at all.

[mof777]

thanks WillRS, i know that we can expect a little rough running but this isnt right and i did say to the dealer it could be carbon build up.

the carbon issue was what i had also thought although have considered the coolant temp sensor but i guess it would throw a code if it has failed

[adsgreen]

hmm... wonder if air leak on the secondary air injection. This will only come in when stone cold.

[WillRS]

hmm... wonder if air leak on the secondary air injection. This will only come in when stone cold.

what part / breaks / wears out / doesn't do its job to cause this if that were the case ?

MRC did have a look over mine when they did the healthcheck and all appeared to be working correctly vaccum system wise and certainly since c/c its definitely a huge amount better..could be coincidence and i suppose could be something else got fixed at same time.

[mof777]

how do you check adsgreen?

[sar]

how old are the spark plugs?, have you ever changed the fuel filter?, how many miles has your rs4 done and has it ever been carbon cleaned?.

[mof777]

cant verify that the sparks have been changed-they were supposedly changed in january
car has 57k
fuel filter i dont believe has been changed and i would suspect its never been carbon cleaned - ive only had the car 5 months

[mof777]

sar

have you had carbon clean? i see that you are north east so would be interested who did it for you

[adsgreen]

Remove the front carbon cover an you'll see a double t vacuum connector.
This supplies the vacuum from under the manifold to
- SAI
- exhaust valves
- manifold airbox flap
- manifold intake flaps

Use a vacuum gauge tester to measure the loss of vacuum on each system

[mof777]

cool - cheers

[EddyPee]

If you are talking about the first mile after just starting, have you tried waiting for the revs to drop before driving off?

Mine was very lumpy on up start, thru 1st to 3rd, especially bad in the cold if you get in and just drive off. I'd had all coils and plugs done and it still did it, now I wait 30 secs or so for the start up revs to drop from about 1300rpm to just under 1000 and I've not had the issue since. Not sure why, I'm sure the boffins can explain.

Worth a try, isn't a fix as such but the jolting is a little un-nerving so I wait.

[doodlebug]

Have you had coolant system pressure tested?

My R32 developed lumpy when cold syndrome, turned out to be head warped and small quantity of coolant had been exiting via exhaust. OK when it warmed up as it expanded enough to seal itself again. Bit of a stab in the dark as I was mega unlucky, I'd not wish that one on anyone!!

[mof777]

not had coolant system pressure checked. just been out in car and i swear its not as smooth as it should be even when its fully warmed too

[nial335]

mine does the same. Full Audi service in Feb (with new spark plugs) made no difference. Mentioned it to Doug when I took my car to MRC for a health check at the beginning of the year. No faults diagnosed by the health check. Doug was familiar with the problem (or perhaps characteristic) and explained the reason why it was like that. It was a bit technical and I can't remember the details but it might be worth contacting MRC about it. On the dyno it made 380 so probably not carbon build up.