LT1 EFI Question

[Roger Heflin]

> 
> 
> <SNIP>
> 
>   The scan tool is an AutoXray Xp240. It does indicate "fan: on". The
> >realtime data seems reasonable. I am only running the primary fan. The 
> >car seems to run very well, although slightly better somtimes. The one 
> >thing that I have noticed that doesnt seem right (other than the fan) is 
> >the idle seems to take a while to settle in. In other words, When you 
> >start the car, It runs a low rpm (mabey 1100). As it warms, it raises to 
> >as high as 1500. But even after the car is fully warmed, you come to a 
> >stop, engage clutch, and its still idling 1300, and then slowly drops to 
> >around 1000. By slowly, I mean several seconds. It never matches the 
> >requested RPM. 
>      
>      Are the requested RPM and engine RPM the same or no? There are *so* 
>      many things you can check, but just for the idle circuit the IAC 
>      motor, the P/N switch, the VSS, the Distributor Reference Signal 
>      (either high or low resolution), etc. If the scan tool is indicating a 
>      requested 900 rpm, yet it is idling higher...I'd check the VSS/PN 
>      circuit first. Did the PCM come out of an auto or manual trans car? If 
>      it was from an auto, you will need to get it flashed for the manual 
>      program. In this case, if the PCM gets a VSS signal, it will raise the 
>      idle to prevent stalling.
>      
>      Later,
>      
>      Larry
> 
> 
> 

On top of what larry said, check the value of IAC, idling out of
gear it should be fairly low.  This controls the air that bypasses
the main throttle body and is how the car controls idle.  It this
value is  0 it means the TB is open too far at idle.  There is a
set screw to adjust this.  Also if there is a large enough cam in
the engine it is really difficult to get it down to a low idle.  My
idle is currently set at 850 (out of gear) and 800 in gear, and cannot
seem to get the idle down that far.  Stock with an auto the
computer will request somewhere around 650 out of gear, and 550 in gear.  If it is requesting much higher that it was probably repogrammed.

				Roger Heflin