Where to look next? Feedback/advice?

[johnb]

I lost track of where things ended up with the TPS. You said the idle switch was not closing, but then I think you weren't sure? I think a quick summary of what we know about that for certain would help. If possible test it at the DME connector.

[spacecad3t]

I lost track of where things ended up with the TPS. You said the idle switch was not closing, but then I think you weren't sure? I think a quick summary of what we know about that for certain would help. If possible test it at the DME connector.

Well, prior to pulling my TB, I did find that some of the high idle was being caused by the throttle stop screw being slightly too tight when hot. That solved the TPS issue. For what it's worth, I have 3 used TPS units, all 3 test fine. I think I have ruled these out.

I thought that solved my idle, but it didn't. So I proceeded to pull the TB to replace the o-ring and clean it up. After this, my idle was 1400, 200 higher than before.

This is where we're at. With the TPS working, TB resealed, the ISV appears to be causing the high idle. Since after disabling it, I have been able to set my idle speed to spec, ~900 with the bypass ~2 turns out.

I test drove it with consumers on and it appears fine, in fact better than before in all regards. At this point Im thinking it's wiring to the ISV? But I am confused why the ISV would be commanded to open this much, unless the car was running so rich it had to?

[johnb]

I lost track of where things ended up with the TPS. You said the idle switch was not closing, but then I think you weren't sure? I think a quick summary of what we know about that for certain would help. If possible test it at the DME connector.

Well, prior to pulling my TB, I did find that some of the high idle was being caused by the throttle stop screw being slightly too tight when hot. That solved the TPS issue. For what it's worth, I have 3 used TPS units, all 3 test fine. I think I have ruled these out.

I thought that solved my idle, but it didn't. So I proceeded to pull the TB to replace the o-ring and clean it up. After this, my idle was 1400, 200 higher than before.

This is where we're at. With the TPS working, TB resealed, the ISV appears to be causing the high idle. Since after disabling it, I have been able to set my idle speed to spec, ~900 with the bypass ~2 turns out.

I test drove it with consumers on and it appears fine, in fact better than before in all regards. At this point Im thinking it's wiring to the ISV? But I am confused why the ISV would be commanded to open this much, unless the car was running so rich it had to?

I'd expect a rich condition to make the ISV close more, not open more. As a rule it opens more in response to the rpm being lower than the idle target, and vice versa. A rich condition will make the idle climb, causing the ISV to cut some air to try to get it back down. But there's a limit to how much it can do that.

What happens if the ISV is installed as normal but you defeat it via the diagnostic port? That disables closed loop ISV control - it'll still open a fixed amount but won't adjust.

[spacecad3t]

What happens if the ISV is installed as normal but you defeat it via the diagnostic port? That disables closed loop ISV control - it'll still open a fixed amount but won't adjust.

I tried this prior to disabling it. There was no change in behavior and my idle screw was fully closed... so there was nothing to adjust.

At this point, I'm thinking it's an issue with my harness? I cleaned the ground connectors and installed new battery/engine ground, but I did not inspect the harness to see if the ground wires are split.

Or the harness connections for the ICV, or even the DME temp sensor? Something like DME thinks its cold, increase fuel, increases RPM, but like you said, wouldn't this cause the ICV to close down?

What else could be causing an incorrect/low RPM reading? I replaced my speed sensor, but my reference sensor appeared fine. Plus my dash is reporting consistently compared with a timing gun...

Last thought. This morning I was testing cold start without the ICV and adjusting the bypass. I went to reposition the capped ICV hose and got a small buzz from the cylinder 1 spark lead. New leads, new plugs, dielectric grease... The air is pretty damp right now, but I have worked on cars in all conditions, rarely been buzzed like that. Would this mean something in the ignition is not grounding correctly or could there be more arcing near the ICV causing noise?

Im grasping at straws maybe...

[johnb]

What happens if the ISV is installed as normal but you defeat it via the diagnostic port? That disables closed loop ISV control - it'll still open a fixed amount but won't adjust.

I tried this prior to disabling it. There was no change in behavior and my idle screw was fully closed... so there was nothing to adjust.

At this point, I'm thinking it's an issue with my harness? I cleaned the ground connectors and installed new battery/engine ground, but I did not inspect the harness to see if the ground wires are split.

Or the harness connections for the ICV, or even the DME temp sensor? Something like DME thinks its cold, increase fuel, increases RPM, but like you said, wouldn't this cause the ICV to close down?

What else could be causing an incorrect/low RPM reading? I replaced my speed sensor, but my reference sensor appeared fine. Plus my dash is reporting consistently compared with a timing gun...

Last thought. This morning I was testing cold start without the ICV and adjusting the bypass. I went to reposition the capped ICV hose and got a small buzz from the cylinder 1 spark lead. New leads, new plugs, dielectric grease... The air is pretty damp right now, but I have worked on cars in all conditions, rarely been buzzed like that. Would this mean something in the ignition is not grounding correctly or could there be more arcing near the ICV causing noise?

Im grasping at straws maybe...

The temp sensor thing was why I suggested checking it at the DME connector before, since if you have no air leak, and a presumably working ISV, that doesn't leave a lot of reasons for the high idle other than a rich condition.

As far as I can tell, the ISV never goes below a 25% duty cycle. When you defeat it via the diagnostic port, it goes to 30% and stays there. So no change (assuming you're sure you connected the right terminals) implies that it was already close to or at it's minimum value.

Physically blocking it off obviously reduces that to 0%. So I'm not sure that this tells us anything about the ISV or the reason for the high idle. Did you check if you can feel it vibrating like I suggested earlier?

I doubt the ISV is susceptible to arcing noise, it solenoid driven and operates at a very low frequency (87 hertz).

As for an incorrect RPM reading being the cause, we can rule that out easily. It couldn't be off by that much without interfering with your ignition timing to the point that the car just wouldn't run. Plus it wouldn't be that consistent.

[spacecad3t]

I did touch the ISV with the key on and engine running, it was vibrating both times and I can hear it buzzing when the engine isnt running.

Ok, I'll test the DME temp sensor at the DME plug when I get a chance.

Really appreciate the help and troubleshooting.

[Tom]

If you are able to smoke test it, I still would do that. I can tune on the fly and my car will maintain the idle at 840 (or whatever it's set to) no matter how rich I run it.

[johnb]

If you are able to smoke test it, I still would do that. I can tune on the fly and my car will maintain the idle at 840 (or whatever it's set to) no matter how rich I run it.

Interesting...I must be wrong about that. I could have sworn I saw a high idle when I induced a rich condition by clamping the fuel return hose, but maybe that was an extreme measure. I might be just adding noise with the whole rich condition thing in that case.

[Tom]

If you are able to smoke test it, I still would do that. I can tune on the fly and my car will maintain the idle at 840 (or whatever it's set to) no matter how rich I run it.

Interesting...I must be wrong about that. I could have sworn I saw a high idle when I induced a rich condition by clamping the fuel return hose, but maybe that was an extreme measure. I might be just adding noise with the whole rich condition thing in that case.

I'll confirm my recollection later this week if still relevant. Have the cluster out right now

[spacecad3t]

If you are able to smoke test it, I still would do that. I can tune on the fly and my car will maintain the idle at 840 (or whatever it's set to) no matter how rich I run it.

I will, but wouldn't that also appear with the ISV disabled/plugged? At this point it goes:
Air box → MAF → Jboot (nothing off of it) → TB → Manifold.