Diagnosing Stepper Motor?

[ammachine390]

That's true too, but even with a bad o2 sensor, the stepper motor would still initialize, and would probably adjust mixture, however, it would adjust it wrong based on a bad sensor signal. It adjusts by just moving the pins back and forth.

[IowaEagle]

Yes, the stepper motor continues to do its thing, even with a bad o2 sensor or a non working/disconnected egr valvel

[Eagleearl]

I would check for a vaccum leak or stuck egr valve.

[RCielec]

Well, this is interesting. The actuator spring of the stepper motor was dislodged, broken in half and jammed into the well it occupies. Was in no postiton to actuate anything. I wonder if a backfire compressed the stepper motor sufficiently to allow the spring to dislodge.
Getting curiouser and curiouser.
Richard Cielec
Chicago, Illinois; U.S.A.

[RCielec]

Ahoy !
Finally got someone to help with the diagnostics. You know the situation: One person to keep the motor running while the other person pokes about under the hood. Anyway..
I think the cause of the problem is found: leaking intake manifold gasket. Sprayed carb cleaner around the joint and heard the idle change dramatically. Intake manifold leak is toward the rear and just in front of the last bolt the secures the intake manifold to the cylinder head.

Thanks to all for your comments. I learned quite a bit.

In truth, I have to think about whether to change the gasket or sell both cars (both have same problem). Frankly, I just don't have the time nor mental focus at present.

Richard Cielec
Chicago, Illinois; U.S.A.