my 87 1.6l fuel injected 323 runs/starts great around town and on
short drives with never a hitch...but when you get it on the highway and run it for
20 minutes or so and then do some stop and go occasionally when you let it return
to idle it will simply die and be very hard to start. If you catch it with the accelerator
and keep the revs up it won't die and will run fine at speed (it never has any problems if you keep the revs up)

Since it doesn't always do it I'm having real trouble trying to figure it out.
Details:
no ac
5-speed manual
new plugs, wires, throttle position switch (checked and rechecked the adj), checked the resistances in the flow sensor as
a function of flapper position

Any help greatly appreciated

 

Sure sounds like an ISC valve (Idle Speed Control). It is located on the throttle body on the underneath side. I bet its dirty and gummed up and needs to be cleaned. If it cannot be cleaned it will need replacing which is rather pricey!