[urq] Stalling at Idle

[Buchholz, Steven]

... sounds like the ECU is leaning things out ... check the OXS duty
cycle ... I'll bet you'll find the duty cycle decreasing as the idle
gets worse.  If your OXS (EGO) is in good shape, you might want to pull
the spark plugs to see if one cylinder is starting to misfire or is
running rich for some reason.  If all that seems to be OK, it may be
that the driver transistor in the ECU for the OXS Freq Valve may be
beginning to fail.  If you don't have a dwell meter you can do the test
where you manually close the WOT (full throttle) switch while the car is
at idle.  This will (should) force the duty cycle to 50% ... I suspect
the idle will return to normal.  This test will also help verify if
there is indeed a problem inside the ECU ...

On the WX the idle bypass is done via the screw on the TB ... no hoses
to pinch.  

Yes, once the engine is warm the OXS feedback loop is closed even at
idle ... 

Steve B
San Jose, CA (USA)
> 
> * After normal warmup the car performs just fine in terms of 
> acceleration,
> cruise, decel and idle.
> * If I sit at idle for about 30 seconds however, the smooth 
> 900 RPM idle
> drops to a very rough condition and will stall if the 
> throttle is not used.
> This just keeps the engine running as holding it at 1200 - 
> 1500 RPM still
> sounds rough.
> * Smooth idle will return after driving for a few miles but 
> degrades within
> 15 to 30 seconds.
> * This problem has been very repeatable and is similar to 
> what happens when
> a vacuum leak is induced, such as removing the dipstick.
> * Have gone through as many vacuum lines as possible and have 
> removed the
> vapor canister purge system to eliminate that as a 
> possibility. Most of the
> other vacuum loads have been removed long ago so the only 
> external line
> feeds the boost gauge & ECU transducer. PCV hose system looks 
> remarkably
> good.
> * Monitoring the EGO confirms that the engine is going very lean.
> 
> Plan to look into the idle bypass system next but looking for anyone's
> feedback. Some simple questions that come to mind are:
> 
>  1) What is the typical EGO VDC at idle? Realize a dwell spec 
> exists for the
> frequency valve but I thought that I remember seeing a good 
> 0.4 - 0.6 VDC
> bounce at idle a few years ago.
> 
>  2) Can I assume the ECU is closed loop at warm idle?
> 
>  3) Is there a simple way to test the idle bypass besides 
> clamping off the
> hose?