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Hi, i have a 2003 RS6 Avant with a 512 bhp MTM upgrade and a full Milltek non-resonated exhaust.

It recently developed a misfire problem under load in cylinders 3 and 7, i had the coil packs replaced and this cured the problem.

Two days later the problem is back again this time cylinders 3 and 4, same again coil packs replaced.

Two days later guess its misfiring again. Can someone help??? Thanks

I guess you are getting P0300/16692 along with cylinder specific errors?

16684/P0300/000768 - Random/Multiple Cylinder Misfire Detected
This DTC indicates that one or multiple cylinders are misfiring, but the ECU fails to identify the cylinder.

Possible Causes

• Air Intake System leaking
  Fuel Supply faulty
  Injector(s) faulty
  Ignition Cable(s) and/or Spark Plug(s) faulty
  Ignition Coil(s) faulty
  Exhaust Gas Recirculation (EGR) Valve (N18 stuck/open
  Camshaft Position Sensor (G40) faulty

Possible Solutions

• Check Misfire Recognition
  Check Air Intake System
  Check Fuel Supply
  Check Injector(s) and Injector Sealing
  Check Ignition Cable(s) and Spark Plug(s)
  Check Ignition Coil(s)
  Check Exhaust Gas Recirculation (EGR) Valve (N18
  Check Camshaft Position Sensor (G40)

All others
Cylinder x Misfire Detected (e.g.)
16692 p0308 035 cyl 8
16691 p0307 035 cyl 7
16687 p0303 035 cyl 3
16686 p0302 035 cyl 2

Possible Causes

• Ignition system
  Fuel injectors
  Fuel pressure
  Running out of fuel
  EVAP canister purge valve
  Evaporative emission system
  Low compression
  Base engine problems
  Controle Module damaged

Are you getting any other errors?

What fuel are you running? Have you tried filling up somewhere else?

When's the last time the plugs were changed?

+What Grant said - especially vacuum + MAF leaks.

Would be useful if you could log the ignition timing to see if it's being pulled by the ECU. Also MAF values.

I was told that you should always change the spark plugs when doing the coil packs otherwise the packs will fail quickly again

chunky79 wrote:I was told that you should always change the spark plugs when doing the coil packs otherwise the packs will fail quickly again

Why?? I'm interested in this as I've just changed a single coil in the wifes X3 yesterday.

I assume is due to the faulty coil not making a full/ proper connection with the spark plug. Spark plugs are pretty delicate

Hi Guys, Thanks for all your replies, i had the car diagnised again and its the original cylinders 3 and 7 misfiring again. I will go with the spark plugs for now although they were changed less than 500 miles ago. The plugs were laser platinums, main dealer supplied with chasis number reference. Could it be the MTM ECU remap playing up?

I doubt the remap would cause the problem unless you have just had it done - best to log some parameters on VAGCOM.