High injection quantity at idle after cold start (2004 BEW)

arcking

Well-known member
Joined
Feb 15, 2017
Location
Western PA
TDI
2x '04 Jetta Wagons (BEW/09A), '13 JSW
Does anyone have any thoughts as to why an '04 BEW would be requiring a high injection quantity to maintain idle after a cold start? It's my understanding that ECU will adjust fueling as necessary to maintain 903 rpm at idle - in this case of my car, this means around 15-20 mg/st (well over 'known good' engines).

What might cause this? I have a couple of ideas below, but am interested in any other thoughts, methods of testing, or confirmation on ideas below:
  • Load on the engine
    • Drag from 09A triptronic transmission, as hinted at in this thread but not resolved
    • Accessory belt - AC compressor, alternator, power steering pump
    • Timing belt - water pump, cam, tensioner (have all been changed and no change to symptoms)
  • Internal resistance in engine (currently running T6 5W-40, same as known good in same environment)
  • Timing - I believe this to be unlikely due to the torsion value being in-spec (and not 0.0), but there's a good read here where a fluke timing issue caused high IQ at idle when cold
  • Low compression- checks out good cold and warm
  • Nozzle/Injector wear/damage - would a poor spray pattern lead to more fuel being injected?
  • ECU reported mg/str doesn't match actual - this seems unlikely given the feedback the ECU gets from the injectors, but I can't say I understand how this plays out.
MVB groups 13 and 23 look good as far as I can tell. This came up in a quest to address an issue I'm having with low power after a cold start (initially discussed here). DanG144 helped point me to the measuring block values in group 1 which I've been closer attention to lately. With an IQ of ~20 mg/st at idle, there's very little room to increase fueling before the smoke limitation kicks in and thus the hypothesis that the increased fueling at idle is an issue.
 
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