Curb idle

[Bitsyncmaster]

How do you set this? How many have it backed out all the way (no screw contact).
Is there a procedure in the manual?

I have my way to set it but just want to know other ways.

[82DMC12]

What do you mean by curb idle? Like where the stop screw touches the plate?

Andy

[Bitsyncmaster]

What do you mean by curb idle? Like where the stop screw touches the plate?

Andy

Yes. It's the lower adjustment screw that prevents the throttle plates from closing fully.

[82DMC12]

OK. Not sure if what I do is correct, but I unscrew both stop screws all the way, allow the throttle to rest fully closed, then insert the lower stop screw. I turn it until it just barely lifts the throttle open so that the butterflys don't bang when you let off the throttle. Then I add the top idle speed microswitch trip screw and turn that one until the switch clicks, add another turn for good measure, then lock it.

Interestingly, I'm dealing with a problem of my own in this area. I have a non-OEM microswitch which I got from a non-DMCH-related vendor. Even though it clicks, it doesn't seem to close the circuit unless the switch is depressed so that it bottoms out. This means it takes much more throttle travel to unclick the switch. Doesn't seem right. I'm going to replace it with an OEM style.

Andy

[David T]

That screw should NOT be touched. It prevents the throttle plates from damaging the bores. It does NOT set idle. The idle motor controls the idle. To properly adjust that stop screw you should remove the throttle section and close the plates lightly. The screw should stop the arm from moving just as the plates are closed and maybe a tiny bit more so you don't force the plates closed. Then lock the screw with the nut and put a drop of nail polish on it. If you feel you MUST increase the idle you can do it by opening the brass screws a little but they should also be closed lightly. Any adjustment of the stop screw or the brass air screws will reduce the amount of control that the idle motor has. If you are not happy with your idle it is most likely due to air leaks and "False Air" leaking into the air induction system AFTER the air sensor plate.
David Teitelbaum

[82DMC12]

David,

When I have messed with that screw before, it's been on cars that have been 'fixed' by PO's who don't know what they are doing. So I definitely know it's not supposed to set idle.

Can you be more specific when you say remove the throttle section? What exactly do you mean, and can you elaborate on how to set it properly if it has been removed or played with? Because you know they always get played with!

Andy

[Bitsyncmaster]

When I had the bad deceleration springs, I had to back the curb idle screw all the way out to keep the idle control working on a hot engine. I found with it backed out fully when I stepped on the clutch the RPM would drop to 500 RPM for a second and then recover to normal. It was suggested that running the curb idle like that caused that undershoot.

I've since replaced the bad deceleration springs and now adjusted the curb idle to 600 RPM with the idle motor fully closed with a hot engine.

So was it the deceleration springs causing that undershoot or something else?

Would it be better to use the air bypass over the curb idle screw?

[82DMC12]

How did you adjust the curb idle to 600 RPM with the idle air motor closed? Now you have me thinking I want to check mine!

Been awhile since I had the W-pipe off. If you have the screw backed all the way out, are the butterfly plates totally closed, or do they start to open up again in the reverse way? As in, they move past perpendicular and start opening backwards? I want to visualize what is happening in there.

Andy

[Bitsyncmaster]

How did you adjust the curb idle to 600 RPM with the idle air motor closed? Now you have me thinking I want to check mine!

Been awhile since I had the W-pipe off. If you have the screw backed all the way out, are the butterfly plates totally closed, or do they start to open up again in the reverse way? As in, they move past perpendicular and start opening backwards? I want to visualize what is happening in there.

Andy

No, the plates will hit the bores in the throttle body with the screw all the way out.

I can set my idle motor closed and hold it there with my new ECU. That lets me adjust the curb idle to a specific RPM. But I found the following is a better way to set the curb idle.

Setting the curb idle screw

The best way I've found to set the curb idle screw is to adjust it with your hot engine idling in neutral and all electrical and AC off. This condition is when the engine requires the least amount of fuel and your idle motor should almost closed. Turn the screw clockwise until your idle RPM is not holding the set idle speed. If you look at the LED on the ECU it should be lit indicating the idle motor is fully closed. Now back the screw out (CCW) a little to bring the idle speed back into the set RPM. The LED should now be off. This setting will give you the fastest reaction time for the idle ECU. Remember if you change your preset RPM value to readjust the curb idle for the new setting.