Hanging high idle

[camaro430sut]

I'm having an issue with a hanging high idle, at or around 1500rpm. One day the car was idleing fine and then the next I get this high idle. The car will start fine, needs no gas to start. Will idle at roughly 800rpm. As the temperature increases so does the idle speed. I cant seem to find any vacuum leaks that would cause this. New o2 sensor. Verified resistance to the thermistor both cold and hot. Verified voltage to the idle microswitch. Running in the garage the car smells very rich. Any ideas are much appreciated.

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[r00b]

Check if the idle speed motor is stuck.

[CFI]

In my experience, a weird idle problem combined with excess fuel in exhaust was a frequency valve issue, which was eventually traced back to a problem in the Lambda circuit. See if the problem goes away when you unplug the O2 sensor.

[camaro430sut]

So I was just thinking. How loud should the frequency valve buzz? Because I don't recall hearing a noticeable buzz sound

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[Bitsyncmaster]

So I was just thinking. How loud should the frequency valve buzz? Because I don't recall hearing a noticeable buzz sound

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If you jump the double yellow/red wires to the brown wire on the RPM relay connector you will power the Lambda system without the engine running. Then it is easy to hear the FV buzz. I do that if I want to drop the rest pressure. Just leave it powered for about 60 seconds and rest pressure drops to zero.

[camaro430sut]

I'll have to give it a go

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[CFI]

So I was just thinking. How loud should the frequency valve buzz? Because I don't recall hearing a noticeable buzz sound

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It’s very difficult to hear it when the engine is running. I usually check its operation by feeling it vibrate. To do that though, you’d need to be familiar with how it vibrates when it is operating normally.

[camaro430sut]

I'll have to start it up later and feel it.

If I drive the car the idle with clutch in coming to a stop will hang as high as 2k. Typically 15/1700. With a load from the a/c it will bring the idle to about 1k/1200

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[camaro430sut]

Any chance this could be cause by the deceleration valves?

Also, I have new o rings and will be cleaning up the previous hacks rtv jobhttps://uploads.tapatalk-cdn.com/20210909/a879623c72b5b4b31ebe05a8b18e5ba8.jpg

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[Acmetowers]

I'll have to start it up later and feel it.

If I drive the car the idle with clutch in coming to a stop will hang as high as 2k. Typically 15/1700. With a load from the a/c it will bring the idle to about 1k/1200

Sent from my SM-G996U using TapatalkI have the exact same issue, idles at 2k when it's warm. If I blip the throttle it drops back to 800. Found out the throttle linkage was out but now wondering if it's the air bypass motors sticking as well.

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[camaro430sut]

I have the exact same issue, idles at 2k when it's warm. If I blip the throttle it drops back to 800. Found out the throttle linkage was out but now wondering if it's the air bypass motors sticking as well.

Sent from my SM-N950F using TapatalkUnfortunately mine will not come down with a blip of the throttle. It high idles but the throttle blades are fully closed

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[Rich]

Yes, there's a chance of that. A good chance. Good of you to post up the open throttle photo of those springs.

Your decel springs look like the ones somebody with high idle posted up about in This Thread (http://dmctalk.org/showthread.php?13145) 5 years ago.

You can save some time by skipping to Post #29 showing a "before fix" shot plus before-after shots in #32. Followed later by a theory about how those springs might have been heated so as to deform like yours did.

In the middle of the thread you'll see some parts source info. from that time.


Any chance this could be cause by the deceleration valves?

Also, I have new o rings and will be cleaning up the previous hacks rtv jobhttps://uploads.tapatalk-cdn.com/20210909/a879623c72b5b4b31ebe05a8b18e5ba8.jpg

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[camaro430sut]

Yes, there's a chance of that. A good chance. Good of you to post up the open throttle photo of those springs.

Your decel springs look like the ones somebody with high idle posted up about in This Thread (http://dmctalk.org/showthread.php?13145) 5 years ago.

You can save some time by skipping to Post #29 showing a "before fix" shot plus before-after shots in #32. Followed later by a theory about how those springs might have been heated so as to deform like yours did.

In the middle of the thread you'll see some parts source info. from that time.Thanks for the link. I actually recall reading that over the weekend d and it's what lead me to the deceleration valves. Glad you pointed me back to it because it gave me an opportunity to reread it. Although our symptoms aren't 100% the same they are relatively similar and worth giving it a shot. I have a line on a used throttle body. However, I'm going to give DPI a call in the am to see if I can get my hands on just the butterflies. They list them on their site but says call for price. Running out of ideas so it's worth a shot!

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[camaro430sut]

If you jump the double yellow/red wires to the brown wire on the RPM relay connector you will power the Lambda system without the engine running. Then it is easy to hear the FV buzz. I do that if I want to drop the rest pressure. Just leave it powered for about 60 seconds and rest pressure drops to zero.Jumped the RPM relay, the FV buzzes I assume as it should. I can see now how one could miss the sound over a running motor, especially at 1500rpm

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[camaro430sut]

So another thing I just thought of. When I last drove it and had the high idle. If I left the clutch out and just crept forward the rpm would come down to about 1k and stay there. This was with the a/c on. Then, once back out of the road driving, push the clutch in coming to a stop and the idle would stay higher, 1500ish

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[Ron]

I'm voting for the deceleration valve springs....

[camaro430sut]

Spoke with DPI. Theyre working in a throttle body for me. Today, I had it running, high idle of about 1500. I noticed if I pressed down on the fuel plate on top of the intake I could lower the idle. Like, it it were open more the idle would be fine. However, im not sure what that points too or how I could achieve that. My dwell meter that I bought arrived and doesn't work. So I can't check the mixture, yet. Just for curiosity sake, I decided to blindly attempt to lean out the mixture. I was able to get the idle to come down to normal. Great, we might be on to something here. Obviously need to go back and check the mixture. Let the car cool off. Went back and restarted it. Instantly to 1500. Wtf, gave up for now. Plan to procure a functioning dwell meter tomorrow

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[Ron]

Just reread everything and have a few thoughts...

Pressing/pumping the throttle doesn't "give it gas to start" (no spray pump like a carb has).

It cold, running rich with good idle, then high idle when warm, sounds like the CO is set extremely rich. (But you should NEVER change the setting until all other things are correct, including idle!)
If you didn't change the setting or anything else before the problem started and have exhausted all of the usual suspects, you might check that the roller that the bottom of the FD plunger rides on is free and does not have a flat spot on it. (I had one that acted similar to this and that was the problem.)

Sometimes blipping the throttle doesn't shut the throttle plates unless you do it right at the shaft, I.E., not with the pedal or other linkage.

I wouldn't put too much into the RPM falling when you press on the plate because that would throw the Air-Fuel ratio off....

[camaro430sut]

Just reread everything and have a few thoughts...

Pressing/pumping the throttle doesn't "give it gas to start" (no spray pump like a carb has).

It cold, running rich with good idle, then high idle when warm, sounds like the CO is set extremely rich. (But you should NEVER change the setting until all other things are correct, including idle!)
If you didn't change the setting or anything else before the problem started and have exhausted all of the usual suspects, you might check that the roller that the bottom of the FD plunger rides on is free and does not have a flat spot on it. (I had one that acted similar to this and that was the problem.)

Sometimes blipping the throttle doesn't shut the throttle plates unless you do it right at the shaft, I.E., not with the pedal or other linkage.

I wouldn't put too much into the RPM falling when you press on the plate because that would throw the Air-Fuel ratio off....Thanks, kind of running out of ideas. I always blip the throttle from the throttle body itself. Car has never required pressing of the gas to start. Tell me more about this potentially flat spotted roller. How do I inspect this?

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[Ron]

IIRC, you can pull the FD and look down into the hole...you'll see what's going on.

Be careful not to let the plunger fall out of the FD and hit anything...

[Rokkinlen]

Having the same issue. Did you figure out what was causing the high idle?

[mhanch]

I had this earlier this summer and it turned out to be my linkage was out of spec. Reset everything and lubed it and the problem went away.