Slight misfire on B5 RS4

[wozza]

I've got the same issue with my RS4. So new ideas welcomed.

Had some diagnostic done on said beast about a year ago which revealed a duff ignition amplifier so changed that which improved matters a bit, but the core issue of slight missfire at low RPM still persists. Then found duff coil pack so changed that - problem still persists.. Checked and changed the plugs also which revealed that on one bank the elctrodes had been worn slightly on one side. Recently changed the lambda on that side as it was reading internal resistance too high (fault code) so I'm wondering if the elctrode wear was caused by lean mixture on that side/bank - so will need to recheck the plugs and see/change them if necessary.

Noticed that using VAGCOM that the lambda on bad bank (bank 2) was noticeably under reading compared to bank one (averaged out plot used as obviously the values swing between too lean and too rich).

* So have changed one ignition amp - in hindsight shouldve done both - but could/can/will still just swap and see if the prob moves.
* Plugs done - need to recheck these for gap and wear.
* Need to resitance check the coil packs on that side to eliminate any dodgey ones.
* MAF was replaced as a matter of course a while ago
* Dump valves changed as a matter of course to forge jobbies.
* All green one way valves replaced as these were faulty - causing air leak in from Charcol Canister
* replaced all solenoid valves as a matter of course.
* replaced cracked purge air pipes as they had been made brittle by the turbo heat (cracked rear drivers side)
* Sorted rocker oil leak to eliminate air leak possibility (p*ssing oil on drivers side bank onto turbo)

Interesting to note that the engine runs much better (but still with slight erratic idle) with Esso or Shell super/vpower. Also Interesting to note that it runs better still with injector cleaner in a tank (with super) - so am theorising a bit about octane rating of sh*t fuel and it being boosted by a hit of kerosene thats in the injector cleaner. Will try an octane booster to see if that helps as well..

Oh yeah also cleaned and reset throttle body which didnt have an effect..

Any other ideas gratefull received.

(Will also be waving the magic bones over the car just in case that helps...)

Cheers

Jon

[Golich]

I hate to say this as it puts the fear of death into me, but it was mentioned to me on the VAGCOM yahoo groups forum. Some time back I asked how VAGCOM detects a missfire. Now I can't remember exactly what was said but apparently it can tell if there is a difference in acceleration rates between the firing cycles. This can be due to a bad valve is what was said to me!

I haven't checked this mainly as both Brooner and my car does this shiver thing rather than a misfire and both our cars make more than stock hp and my case I make an extra 35ftlbs on the stock figures. So I can't see it being a bad valve.

One of the Yahoo forum guys suggested using an oscilloscope as did the service manager of my local stealership (pitty he didn't tell his bloody mechanics to do this the twice the car has been in for a service and I've paid for them to investigate this upon which they have never found a misfire!) It does it all the time as regular as every 10-20seconds at idle but like I say its more of shiver.

[oliew]

my car ticks over smoothly and occasionally does a little shiver then back to normal, its idling at 710rpm according to vag.
no error codes either everything seems spot on, goes well and good fats.
Oli