Can somebody ID this new idle quirk?, starts & runs well -- until warm Options

[Prospectfarms]

(IMG:style_emoticons/default/beer3.gif) (IMG:style_emoticons/default/beer3.gif) (IMG:style_emoticons/default/beer3.gif)

O.K., I'm better now... D-jet is driving me to drink.

The 1.7 starts and runs well until it warms up. After 10 min. idling smoothly @ 900 it hesitates two or three times and stops idling at all, which means I can't keep it running long enough to set the timing. I can keep it going by feathering the throttle, but my nice smooth idle is gone. I reproduced the symptom three times in a row today.

By clamping off the Vac hoses one-by-one it appears the FI components seem to be doing what they're supposed to. No other vacuum or capacitance probs. found so far. Haven't checked the injectors.

This started after I repaired the ground strap on my distributor -- must have bumped something else. CHT?

I have the FI diagnostic checklists and am working on them. If this was a carburetor I'd say it was running with a clogged idle jet (IMG:style_emoticons/default/wacko.gif) . These symptoms seem specific and uncommon. At least I've not seen others posts that describe the same thing. Did I miss one?

[Tom]

From above;
Great info! thanks. Assumed incorrectly that without extra fuel delivery, an open AAR would over lean the idle mixture -- ECU must adjust for proper mixture some other way.
The ECU adjusts fuel mixture based on several inputs, one of which is RPM's.

I think vsg914 has a good test for you, although I would do it a little differently. Start car normally when cold, after about one min, close off the hose to the AAR from the air cleaner by pinching it with some pliers. If the engins stalls, you have the idle set too low. As others have said, with the AAR operating and open, your idle should be 1500 or so.
Tom

[Prospectfarms]

From above;

The ECU adjusts fuel mixture based on several inputs, one of which is RPM's.

I think vsg914 has a good test for you, although I would do it a little differently. Start car normally when cold, after about one min, close off the hose to the AAR from the air cleaner by pinching it with some pliers. If the engins stalls, you have the idle set too low. As others have said, with the AAR operating and open, your idle should be 1500 or so.
Tom

Tom, thanks very much for that clarification. It must seem obvious to you and now it is to me too.

Along those lines, do you know of a document that describes what the ECU "does" with the input from each pin. Manuals and checklists I've seen tend to focus on a description of what each device in the system measures with less detail about how the ECU responds to each signal in order to maintain a "stoichiometric air-fuel ratio".

The TPS must need attention. I think the idle screw is at the end of its travel for it would only turn 1/2, and as vsg914 predicted, that had little effect on idle speed. Though the engine now will continue to run after warm-up, there is little throttle response after the AAR kicks off

Synopsis:My problem was too slow idle during warm-up and then a predictable and sudden stall at 10 minutes. Plugs were fouled. CHT lead had fully or partially ground out. Fixing it (and /or changing plugs) brought the cold idle up from 900 to 1500. Even so, clamping the AAR stalled a cold engine, but a warm engine continued to run without AAR, albeit unacceptably rough and slow (4-500 RPM.) I know that the vacuum system leaks -- the hoses are 25 years old or more. I don't know why the air screw would not turn in more than 1/2. Perhaps it is at the end of its travel and per VSG914 the TPS needs work.

Thanks for all the good advice. There was a lot of it (IMG:style_emoticons/default/type.gif) It really helped.

[Bartlett 914]

I think the idle screw is at the end of its travel for it would only turn 1/2, ........

I know that the vacuum system leaks -- the hoses are 25 years old or more. I don't know why the air screw would not turn in more than 1/2. Perhaps it is at the end of its travel

You must fix all vacuum leaks. The idle adjustment screw is a "controlled vacuum leak". It cannot have a proper effect if the system leaks elsewhere. Fix the leaks first! and adjust the valves.