'98 Civic LX idle unstable; engine dies

'98 Civic LX manual with 94,000 miles.
Symptom: Engine dies instantly when you take your foot off the gas. Symptom is intermittent, but seems to go away after car has been driven for a
while. Once the primary symptom is gone, if the car is left at idle, the idle speed sometimes drifts around significantly.
Recent work, in the past 3 weeks (chronological order) Alternator replaced by indy garage. Plugs and air filter replaced by me. Transmission oil changed by dealer. Frayed wires under intake manifold repaired by dealer (fixed: erratic speedometer, engine light, battery warning light inop) Timing belt replaced by dealer. This included new water pump, 3 belts, coolant, valve cover gasket, etc. [Symptom first noticed at this time (yesterday)] New battery installed by me. [Symptom continued]
Q1. What is the correct idle speed? The tach is mushy at low RPM, but it seems to idle about 500 RPM, occasionally climbing to 1000.
Q2. What controls idle speed? I've seen references to an Idle Air Control Valve. Where is it and what does it look like? Can it be cleaned? What is its expected lifetime?
Q3. Is there an idle air adjustment screw that sets a baseline for the IACV? If so, where is it? Will I get in trouble moving it, as long as I am careful to return it to its current position?
Q4. What else could cause this problem?
This is my daughter's car and I'm ignorant on Hondas and have no shop manual. Any advice will be appreciated.
Thanks, Chris Beall
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Chris Beall wrote:

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Sounds like your reservoir isn't full to the MAX line, and your cooling system may need to be bled of air, too. The rad should be full to the cap, but may have 'burped' since the cooling system was refilled. Be sure you don't add ANY tap water to your Honda (Hondacide). Keeping the reservoir at the right level will insure that the rad will refill itself as any air gets expelled (provided the rad cap is OK) It should be at that age. The temp sensors have to be immersed, and if they aren't, a screwy idle will result.
'Curly'
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motsco_ _ wrote:

Curly,
The reservoir is filled to Max (engine cold). The radiator is full right up to the cap.
Chris Beall
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If I read the list right, the first stop should be the dealer. Two things they did could lead to the problem, which showed up after you got it back from them (did I get that right?)
As 'Curly' says, the coolant could be low - and they worked on that. There is also a chance the timing belt isn't on right, but the straightening out when it warms up makes me put that way down on the list of suspects.
They may not be to blame, but most shops appreciate the opportunity to check their work when stuff like this pops up.
Mike
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Michael Pardee wrote:

Mike,
It goes to the dealer tomorrow, but I don't suspect the work they did. More likely something that has been brewing for a while and my daughter just didn't notice. That's why I'm focussed on idle air controls. I had similar problems on a VW Golf a while back and learned how to keep it functioning, but I don't know if this system is similar nor where the relevant parts are located.
Thanks, Chris Beall
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Chris Beall wrote:

Followup:
Dealer adjusted idle, which has made the car usable, but determined that the Idle Air Control Valve was worn and erratic and was the root cause of the problem. Diagnosis and adjustment cost $68; replacement of the IACV estimated at $300. Dealer did not have part in stock. Replacement will be done in the not-too-distant future.
Chris Beall
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