Irrattic Idle, Closed Loop....
My 1990 k1500 idles high and strong when the vehicle is started cold, despite the weather. Infact it always idles strong in park.
However, in drive, say at a stop light, it idles best up to about 5 minutes after being driven, but then (say if you sit long enough after starting out, like at a long light, or waiting for a train - you can actually feel the idle "kick down", hard. It then idles significantly lower, just high enough to keep running, and idles roughly. Now, it should be noted that under acceleration, it runs smoothly and relatively strongly. However, when sitting back at the next stop light, low, uneven idle.
There are no engine codes, and it seems that this "kick down" always appears to occur at roughly 5 minutes after being driven. Is this the "loop change"? Or can loop change occur even during idle, before the vehicle is driven?
I can't seem to find why the idle changes so dramatically after what appears to be roughly a few minutes driving. I don't know if this makes any sense. I rebuild ever piece of my distributor, new wires/plugs, etc.
Could this have something to do with one of the following?
2. 02 sensor
4. Fill in the blank
You would think that if you had idle problems, they would be present both in park, AND in drive, or under under acceleration, too...but this does not appear to be the case here. It always seems to idle pretty well in park, and for the first few minutes of drive time. It should be noted that there is notable loss of power that seems to come with this "kick-down" of the idle, or so says the seat of the pants. Seems like it is bogging or fighting itself, like it is choking off, or getting too much gas or air. Dunno, only responsive to lots of footpedal, with alot less response with the first 1/2 pedal depression.
The two other possible related symptoms of this "condition" are:
1. it puffs smoke when started in the morning, but only once, and only after sitting overnight. Does not use oil.
2. If you accelerate hard or fast, it will often bog and almost die completely, feels like you floord the brake, not the gas, then recovers as it is floored, and picks up and accelerates as normal.
Anyways, after that windy description, if anyone has any ideas, I am open to them!