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2G Cannot adjust ISC position to 30

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jkuga

Proven Member
140
29
Feb 12, 2017
Oregon
Alright Tuners, I have been dealing with an idle issue since I purchased my GSX in 2017. I am at a complete loss of what to do at this point.
Any advice is greatly appreciated.

My idle has always been sketchy. It feels like it has an intermittment misfire.
When I got the car it was surging. Along with other maintenance items that were changed when I bought it new o2 sensors were installed. This helped but it still is not right.
I have changed the plugs twice to BPR6ES's and new NGK wires as well. Plugs were gapped to 0.028.
I have followed the sigma six idle control guide and am at a loss on how to proceed at this point.
I cannot get my iscpos and learnedidleadj to 30 and 144.
I elimated all boost leaks I found from the throttle body gaskets, injector seals, and had my throttle body rebuilt by TMZ.
I also screwed the FIAV in all the way and elimated a large boost leak from the throttle body freeze plug.
My ISC reads about 42homs when tested which is within spec from what I have seen for a black ISC. I also tested it by turning the key and it does move.

My wideband is also reading around 15 afr at idle never oscilating around 14.7. I do not have it installed in the front o2 location but used a glowshift clamp on bung on my downpipe.
I just don't know what else to check. I want to get this right before moving on.

I have a log of my car up to temp with the BISS screwed in all of the way to get the idle down. But the ISC still won't adjust to the correct position. My tps reads correct at 0.63v.
If I have no boost/vacuum leaks, the isc is good, the FIAV is not a hidden problem, and my tps reads correctly what could be causing these problems?
I've uploaded a video of my wideband at idle and of the sound it makes which makes me think its missing. I've also attached a log.

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  • log.2020.06.03-05.elg
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They’ll be stupid tight because people usually use loctite or peen the back side. My recommendation is to leave those alone at first. Try loosening both nuts on the throttle cable pulley end and the tps first and see if the gap closes. If it doesn’t, then move to the throttle plate screws. When you do them, get the best fitting bit you can and put it in a drill. Put as much force as you can on them and blip the drill. Probably best performed with the face of the tb against a table or hard surface and your drill vertical with some body weight on it. Not too crazy cause you don’t want to bend the shaft. I’ve always set my throttles to be as closed as possible without sticking where idle is Controlled 100% by the isc and BISS.
 
Any tips for getting the screws loose? I've sprayed them down with on blaster, but they aren't budging. I've already stripped one a bit.

I use an impact screwdriver for stuff like that that's prone to stripping out. As jakelandry said make sure they aren't peened before trying to get them out.
 
They’ll be stupid tight because people usually use loctite or peen the back side. My recommendation is to leave those alone at first. Try loosening both nuts on the throttle cable pulley end and the tps first and see if the gap closes. If it doesn’t, then move to the throttle plate screws. When you do them, get the best fitting bit you can and put it in a drill. Put as much force as you can on them and blip the drill. Probably best performed with the face of the tb against a table or hard surface and your drill vertical with some body weight on it. Not too crazy cause you don’t want to bend the shaft. I’ve always set my throttles to be as closed as possible without sticking where idle is Controlled 100% by the isc and BISS.

I use an impact screwdriver for stuff like that that's prone to stripping out. As jakelandry said make sure they aren't peened before trying to get them out.
Alright I'll see if loosening the shaft nuts does the trick and if not attempt to loosen the screws with and impact screwdriver.
 
They’ll be stupid tight because people usually use loctite or peen the back side. My recommendation is to leave those alone at first. Try loosening both nuts on the throttle cable pulley end and the tps first and see if the gap closes. If it doesn’t, then move to the throttle plate screws. When you do them, get the best fitting bit you can and put it in a drill. Put as much force as you can on them and blip the drill. Probably best performed with the face of the tb against a table or hard surface and your drill vertical with some body weight on it. Not too crazy cause you don’t want to bend the shaft. I’ve always set my throttles to be as closed as possible without sticking where idle is Controlled 100% by the isc and BISS.

Alright I loosened both nuts a whole turn. The throttle plate does look more closed but the nut on the tips side is pretty loose now. Also you can see light more toward the tps side than the pulley side. Maybe I still need to recenter the plate?
Here's a before and after of loosening the shaft nuts.
Before:
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After:
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It would make sense that this is where my leak is because all my recent boost leak tests I lose pressure quickly from the oil cap. Which I know is normal but if the throttle isn't closing all the way than it would make sense that it's letting more air in and that is leaving through that cap right?
 
Alright I loosened both nuts a whole turn. The throttle plate does look more closed but the nut on the tips side is pretty loose now. Also you can see light more toward the tps side than the pulley side. Maybe I still need to recenter the plate?
Here's a before and after of loosening the shaft nuts.
Before:
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After:
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It would make sense that this is where my leak is because all my recent boost leak tests I lose pressure quickly from the oil cap. Which I know is normal but if the throttle isn't closing all the way than it would make sense that it's letting more air in and that is leaving through that cap right?

The pressure test is a different ordeal.

You can try tightening the side nut to pull the shaft back center but if both nuts are loose and it still has a gap at the top and bottom you have 1 of 2 things going on. Either the throttle stop is stopping it prematurely, or the plate is not completely centered. You can try backing the throttle stop off some and let it slap closed to see if that’s preventing it. If the gap doesn’t close you’ll need to adjust the valve. Once you break it loose, I recommend slightly tightening the side nuts evenly to center the shaft back up. Just don’t tighten on them too much cause you’ll pull the shaft to one side or the other and it will catch.
 
Simulate the plate opening and closing fully. Is it smooth or does it hang up?

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The pressure test is a different ordeal.

You can try tightening the side nut to pull the shaft back center but if both nuts are loose and it still has a gap at the top and bottom you have 1 of 2 things going on. Either the throttle stop is stopping it prematurely, or the plate is not completely centered. You can try backing the throttle stop off some and let it slap closed to see if that’s preventing it. If the gap doesn’t close you’ll need to adjust the valve. Once you break it loose, I recommend slightly tightening the side nuts evenly to center the shaft back up. Just don’t tighten on them too much cause you’ll pull the shaft to one side or the other and it will catch.

I backed the stop screw back two full turns and tightened it down.
Here's a video of it opening then snapping closed. Doesn't appear to catch, stick, or bind in anyway.

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Here's a new photo now with the screw back out. You can no longer see a ring of light. Just the barest ring when looking at it from the side maybe around the shaft.
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Be careful. That one screw is funar’d and you don’t want that going through the engine. Use a larger phillips if you have one.
Yeah I got a little over excited yesterday and tried to do it without an impact screwdriver. If the plate is closed now though I should be ok to leave it right?
 
Well I just tried it again and it does take just the smallest extra bit of force to start opening it again after letting it snap closed. Is that the binding that has been referred to?
 
Well I just tried it again and it does take just the smallest extra bit of force to start opening it again after letting it snap closed. Is that the binding that has been referred to?
No binding would be plate snagging during or preventing movement, you need to retighten the stop screw ever so slightly. The stop screw is there to let the throttle body stay "open" or cracked ever so slightly. I normally screw in the throttle stop screw by hand and after making contact, give it half a turn with a wrench.
 
Looks good to me too. If you hit the screw with an impact it shouldn’t come loose. You might have tweaked it ever so slightly from not sitting straight.
Are you referring to the plate screw or the stop screw? Neither were hit with an impact. I stripped the plate screw a bit with a normal screw driver and for the stop I just used an 8mm wrench to bust the lock nut and then turned the screw by hand.
 
Are you referring to the plate screw or the stop screw? Neither were hit with an impact. I stripped the plate screw a bit with a normal screw driver and for the stop I just used an 8mm wrench to bust the lock nut and then turned the screw by hand.

I was referring to the screw for the plate. You’ll be fine as long as it’s tight
 
Yeah that sucker didn't budge haha. I sprayed some pb blaster on them but I didn't even touch the one after I stripped the other.

I'll get the throttle body back on and see if the isc adjusts. Fingers crossed.

I booger’d one screw for the fiav and learned my lesson so I always use an impact with the correct size phillips. This should fix your issue. Keep us posted
 
Alright looks like moving the stop screw did it! I'm super grateful for everyone's help. This has been a thorn in my side for a while now.
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After I first set the biss it read lean 18-19 afr at idle. However after taking it for a cruise it moved to 14.7-15.
Looks like I'm ready to move on to the next thing.
 
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