Iac position?
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You can "slot" the holes of the TPS to rotate it back if opening the TB blades does throw the VDC of TPS out of spec
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This from a post I kept years ago:
You will often get better idle quality with an aftermarket cam by closing the throttle body stop screw as far as possible without the throttle blades sticking when closed. This takes better advantage of the idle air passageways in the TB/intake/heads, as well as the IAC valve. Once you adjust the screw, you will probably need to reset the TPS, so that it outputs between 0.55V-0.66V when closed, with the ignition on and engine off (slot the TPS screw holes to adjust it by turning). You would then need to use a scan-tool of some type to check the IAC counts at idle; they should be in the 20-30 range. If they are higher, open the TB blades further again, or drill out the idle air hole in the TB very slightly, until they get into that 20-30 range at idle. If they are much lower, close the TB blades even more if possible.
You will often get better idle quality with an aftermarket cam by closing the throttle body stop screw as far as possible without the throttle blades sticking when closed. This takes better advantage of the idle air passageways in the TB/intake/heads, as well as the IAC valve. Once you adjust the screw, you will probably need to reset the TPS, so that it outputs between 0.55V-0.66V when closed, with the ignition on and engine off (slot the TPS screw holes to adjust it by turning). You would then need to use a scan-tool of some type to check the IAC counts at idle; they should be in the 20-30 range. If they are higher, open the TB blades further again, or drill out the idle air hole in the TB very slightly, until they get into that 20-30 range at idle. If they are much lower, close the TB blades even more if possible.
Not sure who wrote that, but drilling that hole out is not necessary for a small cam. Hard to undrill a hole if you go too far. It is needed for a big cam, not a small cam, like the LT4 "Hot" cam, etc.
What would you consider a big cam? I'm running the xfi 292 in a 396 and have the stock sized hole in the tb with no idle issues. Used the same tb with a solid roller only slighty more aggressive as well.
It's an honest question. Not trying to say my cam is large or anything of that sort.
It's an honest question. Not trying to say my cam is large or anything of that sort.
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Verdad Gallardo What would you consider a big cam? I'm running the xfi 292 in a 396 and have the stock sized hole in the tb with no idle issues. Used the same tb with a solid roller only slighty more aggressive as well.
It's an honest question. Not trying to say my cam is large or anything of that sort.
It's an honest question. Not trying to say my cam is large or anything of that sort.
On another note is the 30's suppose to be in closed loop? Mine starts off at around 100-115 then drops to around 30-33 but then will max out I thing I need to open the blades some more.
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Mine and 2 friends who has almost the same set-up is the same. I don't know what he's doing to the tune or if it's the bigger cam.
On another note is the 30's suppose to be in closed loop? Mine starts off at around 100-115 then drops to around 30-33 but then will max out I thing I need to open the blades some more.
On another note is the 30's suppose to be in closed loop? Mine starts off at around 100-115 then drops to around 30-33 but then will max out I thing I need to open the blades some more.
This from a post I kept years ago:
You will often get better idle quality with an aftermarket cam by closing the throttle body stop screw as far as possible without the throttle blades sticking when closed. This takes better advantage of the idle air passageways in the TB/intake/heads, as well as the IAC valve. Once you adjust the screw, you will probably need to reset the TPS, so that it outputs between 0.55V-0.66V when closed, with the ignition on and engine off (slot the TPS screw holes to adjust it by turning). You would then need to use a scan-tool of some type to check the IAC counts at idle; they should be in the 20-30 range. If they are higher, open the TB blades further again, or drill out the idle air hole in the TB very slightly, until they get into that 20-30 range at idle. If they are much lower, close the TB blades even more if possible.
You will often get better idle quality with an aftermarket cam by closing the throttle body stop screw as far as possible without the throttle blades sticking when closed. This takes better advantage of the idle air passageways in the TB/intake/heads, as well as the IAC valve. Once you adjust the screw, you will probably need to reset the TPS, so that it outputs between 0.55V-0.66V when closed, with the ignition on and engine off (slot the TPS screw holes to adjust it by turning). You would then need to use a scan-tool of some type to check the IAC counts at idle; they should be in the 20-30 range. If they are higher, open the TB blades further again, or drill out the idle air hole in the TB very slightly, until they get into that 20-30 range at idle. If they are much lower, close the TB blades even more if possible.
The way I set idle is, first turn off, or block the IACV passage of the engine. This way all the air going into the motor is coming from NON-iACV sources. Then, say I want the idle to be around 550rpm, I would set the idle manually to about 510rpm fully warm (using throttle body blade usually). Then, re-connect the IACV and let it take up the final 40-50rpm of idle speed. Open just a tiny bit when the engine is warmest.
Whoever wrote that piece about closing the throttle blades completely has no idea what they are talking about.
Only way a bigger cam LT1 would idle well that way is if the hole between the throttle bores (stock casting was enlarged. The IAC simply can not pass enough air alone for a larger cam, larger engine. You have to open the throttle blades, or drill holes the the throttle blades, like is often done to carburetors with larger cams. Down side is you can not undrill holes if opened too far. I have observed very small differences in variations in cylinder balance done wither way. DIY guys can more easily just crack the throttle blades open a little more.
Only way a bigger cam LT1 would idle well that way is if the hole between the throttle bores (stock casting was enlarged. The IAC simply can not pass enough air alone for a larger cam, larger engine. You have to open the throttle blades, or drill holes the the throttle blades, like is often done to carburetors with larger cams. Down side is you can not undrill holes if opened too far. I have observed very small differences in variations in cylinder balance done wither way. DIY guys can more easily just crack the throttle blades open a little more.
Last edited by Ed Wright; Jul 29, 2017 at 09:38 PM.
How far should you have to open them? I read the same thing and it said to open them 1/4 -1/2 turn. I tried that and still haven't gotten the idle set right.
Last edited by 92camaroguy; Jul 30, 2017 at 07:46 AM.
You also have to take your TPS position into consideration when opening up the blades. I have my blades open just enough to see daylight and I have no issue. What is your idle set at tune wise?
Yeah the TPS volts are in range .70 and at WOT it's 4.75 I thought 4.5 was max? My idle is at 850 but hardly sees it.
Out of somebody's butt, I'm guessing. It is not in any of my original GM shop manuals. Some cheaper scan tools don't show all the available parameters, so may give TPS volts, and not percent TPS. Open it to one percent, it won't want to idle back down. Bigger the cam, more tweaking needed to make it idle well.
LT1& LT4 manifolds have an idle air passage from that hole you see between the throttle bores, that opens into each intake runner. Really big cam (needing to idle like 900 + RPM) opening that hole some works very well for a stable idle.
And, simply setting the idle speed up in the "tune" is not all there is to that part of it either.