[urq] Stalling at Idle

[Rick Petrow]

Greetings from the Amish country,

	For the past few weeks the idle quality has become an issue and I’m looking
for some ideas. Car is an ’83 with many miles but has been very reliable for
the past few years. Granted the weather is not ideal for driveway
diagnostics but “3-footing” the pedals to keep the car from stalling is
getting to be a drag. Since I drive the car almost daily in the winter the
symptoms have been easy to remember as the problem is also very consistent.

· 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?

 4) Have added a bottle of Techron and 3 - 4 tanks of fuel to eliminate
gaoline as a source.

   Many thanks in advance.