Initial idle tied to ambient temp

Ok, head scratcher here. '79 K-ket car B21F, M46 w/aux air valve.

I can't dial in a consistent cold start idle - it seems to be tied to the outside air temp. I've tested the Aux air valve w/the usual fridge/warm water tests and it seems to respond ok. Cleaned it out with carb cleaner, gave it a good shake.

Weather has been up and down the last few days, so mornings are still low 40s and afternoons can get near 80. Car will jump right to 1200 RPM when starting in the morning. Start it in the afternoon and it idles around 600, almost stalling out until it warms up and gets back up near 1000. If I then adjust the idle screw to get it closer to 1100 or 1200 all is well until the next cold morning, when it idles at 1500, etc. Once it's all warmed up the idle is rock solid at least, no hunting/dipping/etc.

I'm also not sure how much I should depending on the throttle adjustment to set idle - it's supposed to fully close and then open back up 1/4 turn, right? Checked for vacuum leaks and there aren't any. I'm stumped...

I'm not a kjet person but if I think logically about this...

In general, if your car idles better when it's warm (and we're talking about these sorts of temps rather than freezing/oil viscosity issues) I would look for potential seal or sealing issues. They may only present when cold btw.

On the other hand, the air would be less dense in the afternoons and maybe you're putting a touch too much fuel in on the cold idle that gives it troubles?

I'd probably wait on someone with legit kjet knowledge though...

EivlEvo said:

On the other hand, the air would be less dense in the afternoons and maybe you're putting a touch too much fuel in on the cold idle that gives it troubles?.

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I've got a wideband on it and it runs rich for just the 15-20 seconds that the cold start injector is on, and right around lamda afterwards. Got it dialed in just right so that it bounces between .98 and 1.02 or so.

Bricktothefuture said:

I've got a wideband on it and it runs rich for just the 15-20 seconds that the cold start injector is on, and right around lamda afterwards. Got it dialed in just right so that it bounces between .98 and 1.02 or so.

Click to expand...

But that's reading it being stoich in the exhaust stream... if you have a vac leak someplace the reading is correct, just not correct for the motor.

EivlEvo said:

But that's reading it being stoich in the exhaust stream... if you have a vac leak someplace the reading is correct, just not correct for the motor.

Click to expand...

Ooh good point.

In my experience the aux air valve is probably out of adjustment. There is a small nut and screw on the valve that lets you adjust the position of the valve. A 1200 rpm idle in the warmer weather like this is too high. Try closing the valve slightly when cold. Go for something like a 1k rpm cold idle. Just move it a little at a time till you get it where you want it.

The warm idle is adjusted with the plastic thumb by the throttle body. There is also an adjustment for the resting position of the throttle plate. You want it to close and just touch the adjustment screw to the linkage arm then a quarter turn or so. Then after that the idle should be adjusted with the thumbscrew.

Before you do any of those adjustments. Be sure the ignition timing is correct. Timing belt at proper tension as well. Loosen the tensioner a full turn and torque to 36lbft.

dl242gt said:

In my experience the aux air valve is probably out of adjustment. There is a small nut and screw on the valve that lets you adjust the position of the valve. A 1200 rpm idle in the warmer weather like this is too high. Try closing the valve slightly when cold. Go for something like a 1k rpm cold idle. Just move it a little at a time till you get it where you want it.

The warm idle is adjusted with the plastic thumb by the throttle body. There is also an adjustment for the resting position of the throttle plate. You want it to close and just touch the adjustment screw to the linkage arm then a quarter turn or so. Then after that the idle should be adjusted with the thumbscrew.

Before you do any of those adjustments. Be sure the ignition timing is correct. Timing belt at proper tension as well. Loosen the tensioner a full turn and torque to 36lbft.

Click to expand...

Good stuff, never tried to adjust the actual aux air valve, always just used the knob on the throttle body. Ignition timing is around 12-14 deg, cam gear is 2 deg advanced. Will try that adjustment.