[s-cars] Short term rough idle - follow-up

[john at westcoastgarage.net]

Louis-Alain Richard wrote:
> But then, it may be the ECU cold running enrichment feature, and that one
> may be time-related instead of temp related. So, if the temp sensor is bad
> and tell the ECU that the engine is hot, that may cause a rough idle for a
> few seconds ?
>
> Louis-Alain
>
>
>
> -----Message d'origine-----
> De la part de Robert Myers
>
> Maybe, Vittorio, but I kinda doubt it.  The time interval is so short 
> that there is little perceptible temperature change at all in the few 
> seconds duration.
>
>
> At 12:16 PM 1/25/2010, Bares, Vittorio wrote:
>
>
>   
>> Seems engine temp related - could it be the sensor?
>>
>> Vittorio -
>>     
>
>
>   
Old, tired, injectors frequently pass a little fuel after shut down, 
some quickly, some over an extended period of time. This is especially 
true of CIS or "mechanical" injectors.  In the cylinders with open inlet 
valves, the fuel puddles on the piston top, in cylinders with the inlet 
valves closed it sits on the valve.  As modern fuels are substantially 
less volatile than those of days past (especially the "winter" fuels), a 
significant quantity of un-atomized fuel momentarily fouls whatever 
cylinder we're talking about, and the engine runs rough until it clears 
the flooded condition.  It doesn't take much fuel to cause this, and 
temperature only plays a role as a function of time.

John