Atypical high idle issue

[Cloud]

So I have dealt with high idle problems quite a bit in the past and had been having pretty good luck up until now. The issue here is not leaks, fiav is blocked, tb seals replaced, etc... The issue is the isc is actually stepping when it shouldn't be. Normally I would assume this means my idle switch is not working, but I cleaned it out and it is making solid connection but still having no effect on the isc duty cycle one way or the other, I have tapped the idle switch line to verify it is getting voltage when the throttle is shut and it is. It revs up at first then the isc idles down to about 10.5% on the logger and will go no lower regardless of the conditions. The idle switch seems to have absolutely no effect. Is this a sign that the wire might have a problem and I should try to check the pinout at the ecu or is there something else that might cause the ecu to open the isc when it shouldn't be?

[yokotabrat]

EGR blocked? Did you follow the factory procedure for setting the idle switch? If not, it's possible that it's holding the throttle plate partially open.

Have you ever had any isc coils shorted or low resistance? Caps leaking in the ecu or anything? I have a little tester that could determine the condition of the 2 ecu isc drivers in 2 minutes if you wanted to rule that out.

[Cloud]

My isc has always been solid. Everything but the isc has been blocked off properly and I have verified that the idle switch adjustment is not the problem by removing it entirely and having almost no change. I have never had the isc stay at 10.5% though, especially not since I set the biss so that it was at approx. 0% at warm idle with accessories off and correct idle speed.

I have been reading a ton of crap and I am beginning to think that the vss may have crapped on me. I logged it and it randomly bounces from 2 to 130 on the logger. I have no idea what those numbers mean but I assume it's not normal operation for it to do that whether the vehicle is moving or stationary. I didn't even realize the 1g has a vss as it's mechanical and it looks like some stupid reed switch in the cluster or something? Anyone have experience with this?

[yokotabrat]

The only issue I've ever heard of when the VSS goes bad is the car will have the tendency to stall when coming to a stop. The VSS is indeed a reed switch in the back of the cluster.

The ecu does have a rolling idle correction where it will raise the idle about 250rpm when the car is moving, so I guess that's possible. I thought I've logged the vss on mmcd and gotten the same thing you're seeing, but I'd have to check when I get home to see if that's true. Maybe it's not logging the correct address?

What rpm does your car idle at? Does it surge?

[Cloud]

It's idling at around 1000-1300rpm depending on temp and how it feels now when the logger reads 10.5% isc. It does not have the characteristic surge. Just high idle, something I would normally attribute to idle switch, I don't have my blinky light anymore so I can't tell if it's fuel cutting on decel, that damn blinky light was more useful than people give it credit for haha. vss and idle switch are about the only 2 things I can think of non-accessory related that control the isc. The cts has some fluctuations but it makes about a 0-4% difference, and has no bearing on the 10.5% it will not drop below now.

[yokotabrat]

Thinking about this some more, I'm not sure it could be the vss. Since the vss is a reed switch, it's either going to be closed or open if it's gone bad. The ecu looks for pulses, so if the vss is bad and it's not pulsing, the ecu won't put it into a higher idle like it normally does.

There's a pretty quick way to test the ecu drivers to make sure it works. Reset the ecu by pulling the battery terminal. Then unbolt the isc and lay it somewhere where you can watch the isc pintle. Turn the car to "ON" but not start so that the ecu powers on. The first time the ecu is powered on from being reset, it "homes" the isc, so your isc should click for a second or two and move slightly in. If it doesn't move or make any noise, one or more of the drivers in your ecu may be damaged.

[Cloud]

I guess the real question here though is why is the ecu still trying idle up the car with the 10.5% isc step when it is above the normal idle? Even if the isc or ecu drivers were failing wouldn't the ecu still try to maintain the correct idle speed unless it were receiving an improper signal from one of its sensors? I thought a failure of the isc led to low idle and surge as the ecu attempts to correct it not just a static high idle?

[Cloud]

Ok, update. I found a vacuum line for my cyclone controller unplugged... this had roughly no affect on the idle lol. I also noticed some stuff, one of which being that my stutterbox will not select with input to the gas pedal. I'm not sure what switch keydiver uses for this but I would imagine it's probably the idle switch, meaning I am possibly not getting that signal at the ecu then even though it's good at the connector/wire in the engine bay. I'll keep this updated and if anyone wants to throw out more ideas I am entirely willing to hear them as this is still very irregular.

[Kibo]

Have you checked the ground at your throttle body housing? It's possible the idle switch is functioning but there's no ground at the TB itself.

[Cloud]

Yeah, I have verified with a multimeter that it has continuity. I even tapped the wire itself to see if it was a corroded connection but all seems well. I talked to keydiver and the stutterbox does in fact use the idle switch. I guess intuition was still correct in thinking this was an idle switch problem but now it has me worried the ecu might have an issue. I am praying for an obvious break in the wire somewhere easy to fix :D