it definitely sounds like somethings wrong with the fuel pump or even just the fuel filter is clogged.
Well, considering we're digging this thread back up, I investigated the fuel delivery side of things some time back.
It's definitely not a fuel pressure problem (on my KA anyway), from key to On to idling for approx 1min then a short drive round the block, the fuel pressure never dropped below the minimum as stated in the FSM.
I still get a similar (but not as harsh) stumbling from both my U12's, but it's very periodic these days. That being said, for it to be a fuel issue, it would have to happen all the time. I don't believe it is related to any aspect of the SCV system either (which has the ability to potentially cause similar symptoms) because my black U12 has this SCV system deleted completely, whereas it is still fully intact on the daily TRX.
It's not something that can be isolated to the ecu either.
I tend to think it's an electrical issue that I have yet to find.
just my two cents, letting the engine idle for extended periods before driving is actually worse than driving straight away... at idle the fuel mixture is higher than at optimum revs, meaning unburnt fuel can often get through and do all sorts of shite over time.
Dr Karl told me.
This statement makes no sense....when an engine is cold and started, the ecu is comparing the coolant temperature it senses in the engine to a fuel enrichment table in the ecu, and consequently injects more fuel if the engine is cold. This is known as "cold start enrichment" and is found on every EFI engine in existence. It's a known fact that cold engines aren't too happy when they are at their coldest.
As the temperature increases, the amount of fuel is reduced until the temperature threshold for determining "cold start enrichment" is met and the normal fuel / idle tables are used.
Idling a cold engine for a few mins allows your oil temps to come up to assist in preventing damage to all of your important rotational components within the engine.