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Hi,
From what you are saying it appears that this is a lean mixture at idle when it’s the engine is still cool to cold.
Due to the year this should be the LH 1.0 in the USA. As the number implies it’s the first generation controlling a B 23 engine. Turbocharged ones were around but not mentioned here or past posts in your profile.
During startups and the warming up program in the computer the “Idle Air Control” must have complete control of this low air intake speed.
It is trying to adjust for a cold engines friction within “presets” within its fuel management program for the call to “idle.” Start, warmup and operating temperatures with some other input variables.
These come from the “throttle switch” and watching the idle speed from the distributor and ICU box.
Later on the oxygen sensor is considered.
It appears that it’s doing just what it’s supposed to do, by trying to recover, but eventually not able to do it fast enough and slowly loses the battle.
With each restart, the engine “does” get some heat to work with and it loosens up. A bigger factor in winter.
What You don’t want is any air from any other vacuum lines coming into the intake manifold ports. This is primarily from the throttle plate position and the Flame Trap system. Lesser is cabin vacuum influence from a source hose or one to the fuel pressure regulator if acceleration is an issue there.
You are saying it’s fine @ operating temperature.
These symptoms, Under most circumstances, the above causes to much air during low air intake speeds behind the AMM that located behind the air filter and in front of the throttle body.
Any air not measured by the AMM is unknown by the computer program and this is a big factor!
A tiny pin hole or a loose fit of the accordion tube between the two is the first place of a possibility.
From there we look for a “dirty throttle body” or the throttle plate open any “at all” while the throttle switch needs to be telling the computer to idle!
This switch gives the computer a “heads up” that the driver wants to accelerate and needs to jump to another program in succession!
If this switch and plate are need to be in time together.
The IAC has a limited range. The throttle setting needs to be the middle of the range of open to closing!
Once they are set together, the response and the “transition area” into powering up, from idle, becomes a properly controlled engine!
This is happening on this engine when it has enough heat and faster responses due this new condition.
It appears that the computer control with the other inputs working correctly to your satisfaction?
The oxygen sensor is the only way the computer knows that it is dialing in the proper emissions!
This mode is called “closed loop” of feed back and is now self tuning!
So during the conditions, you have stated, you need to look fo excessive air or some adjustments to put the air system within the computers program part.
If you are having a misfire, due to lean mixtures, the computer will try popping open the IAC and adjust timing at the same time and you might be hearing a clack and knock while it’s trying to recover but that can kill the engine.
Sometimes, I think it could be a default, to just start all over!
The newest cars call it a “reset” or an engine light if it happens enough times!
They do this to tell the owner... “You might be able to ignore me, but I will remind YOU!”
The engine is “talking to you” here and it is getting your attention without the CEL and any COSTS associated with all that SNITCHING! (:-)
I see you are new to the board and I think you have done a good job getting your question across.
So in further posts, you might put in more car details of maintenance conditions for all to consider into the symptoms.
There could be other things to consider, as we are all using our” armchairs.”
Most of us like using our “check off listings” for a symptoms in our minds so questions arise.
There are several minds on the Brickboard “to pick through” and some are in FAQ’s searches of your term of “internet wisdom!” (:-)
Thanks for yours!
Phil
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