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PostPosted: Tue Jan 05, 2016 3:23 pm 
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Location: Lowell, MA
Here are the symptoms:

On cold start revs are ~2k, no surge
Drive for 5 minutes until engine is warm
Idle is rock solid 800-1k rpms
Decel on highway is...not great, jerky at times

I have checked:
TPS (closed, partial, WOT) good
ISC opens+closes when warm, good resistance, passage clear
Cleaned MAF element
Vacuum hoses inspected
O2 sensor (video of test)

So what next? It looks like there is a FIAV valve on the back of the intake. Does this control the cold start idle at all?

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PostPosted: Tue Jan 05, 2016 5:47 pm 
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Location: NW Indiana
The fast idle valves(thats the one on the firewall side of the intake) do have a tendency to leak with age. I would block it off and see if that fixes it. I think you can still get new ones from rockauto, though they are kinda pricey. I just left mine blocked, other than a lopey low idle when cold it works fine without it.


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PostPosted: Tue Jan 05, 2016 11:03 pm 
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kzelisko wrote:
The fast idle valves(thats the one on the firewall side of the intake) do have a tendency to leak with age. I would block it off and see if that fixes it. I think you can still get new ones from rockauto, though they are kinda pricey. I just left mine blocked, other than a lopey low idle when cold it works fine without it.


Good to know, thanks. I will try your suggestion. Thankfully most of my knowledge from 1g DSMs a decade ago translates well onto this car. Same tech. Same problems, haha. If it is leaky...can it be fixed?

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PostPosted: Thu Jan 07, 2016 12:10 am 
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Location: Mount Vernon, WA
Did you do the pinch test on the ISC? Run through the test for what you are calling the fast idle control valve. Cold the valve should be open and hot it should be closed. You can visually see this with the elbow off the end. There is also a bench test that requires you to dump in hot water. I imagine these can get worn out where the valve no longer seat. I believe someone currently is selling one.


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PostPosted: Fri Jan 08, 2016 10:02 am 
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I didn't do the pinch test but I did disconnect the bottom port (intake), plug it with my finger, then energize the coil with 12V, and release my finger. There was an inrush of air but I guess that doesn't rule out a blockage in the path...I'll continue down that path a bit.

I plan on yanking the Cold Air Valve, blanking it, and test it in some water. That's a great idea!

I just re-did my ground wires from the battery with some high quality wire. Oh boy did that make a difference! It didn't solve my idle issue but it helped. What it mainly did was increase my low RPM throttle response by ~20%. If you have any doubts about your grounds replace them ASAP.

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PostPosted: Sun Jan 10, 2016 10:47 am 
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Has anyone thought of making an aftermarket CAV? If you made an adapter plate to a voltage controlled valve you could have the valve open at a certain temperature.

Image

This would cost pennies on the dollar for a new CAV. A few questions on how the CAV actually works...

What type of flow rate is going through the valve?

Is it an OPEN/CLOSED valve or is it variable with temperature?

What temperature does it open at?

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PostPosted: Sun Jan 10, 2016 12:42 pm 
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I believe it varies with temperature up until the point it closes. That being said, I think and on/off would work fine as well, plenty of 80's cars worked that way. Judging by the way the engine reacts to it being blocked I'd say the ecm pays no mind to what the cold start valve is up to, mine idles right at curb idle, hot or cold, and it doesn't set any lights or make it run weird.


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PostPosted: Mon Jan 11, 2016 11:24 am 
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I'll start with the delete and go from there. Thanks!

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PostPosted: Wed Jan 27, 2016 5:16 pm 
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I have made some progress, that said my idle is the same.

I fabbed up a blocking plate but I'm not really happy with that solution. I am attaching a 12V vacuum solenoid to the plate that opens at a set temperature using an Arduino Uno board for all the heavy lifting. I finished with the circuit design and made a little video demonstration.

I wanted to be able to get an idea as to what the temperature was and when my idle started to behave normally. I setup 5 LEDs that sequentially light up as the voltage/temperature changes. Then from another digital out pin I went to a 5V relay that switches the 12V(car) power to drive the vacuum solenoid with a yellow ON indicator light. You can see the little vacuum solenoid next to my setup in the video. Thank god for the massive surplus we have in lab.

https://youtu.be/sqpDG65NrcQ

Once I get a handle on temperature settings I'll finish the plate fabrication and see how she reacts...

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PostPosted: Wed Jan 27, 2016 5:49 pm 
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i have a different engine, g10t, running on a megasquirt which i have set up to delete the turbo3's cold start injector and run regular fuel enrichment for the cold start and warm up off the main injectors. it should be very similar to what you're doing.

the curve i have programmed in 5 steps varies the pulsed solenoid opening from wide open at below 100 f to fully closed at 160 f. i have the coolant operating temp set at 180 f and run a 180 f t-stat.

my red twincam vert started giving me idle problems and i had no qualms about the idle actuator delete. i pulled the valve off the back of the manifold, installed the delete plate, and never looked back. :wink: now when i start the engine it goes directly to an idle of 850 rpm and never changes. the idle air is still modified by the idle solenoid.

to be fair, the twincam vert is a summer only car. i rarely drive it in temps lower than around 60 f.

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PostPosted: Wed Jan 27, 2016 8:21 pm 
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t3 ragtop wrote:
the curve i have programmed in 5 steps varies the pulsed solenoid opening from wide open at below 100 f to fully closed at 160 f. i have the coolant operating temp set at 180 f and run a 180 f t-stat.

to be fair, the twincam vert is a summer only car. i rarely drive it in temps lower than around 60 f.


Good info. The flow through the little solenoid I have is pretty small so I was thinking of putting 3 solenoids that open at different temperatures. This really only rears its head in <40 F days, which in New England is a good many days.

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