Explain how the idle air system is currently known to be ran in the Gen4 ECUs

Been chasing issues with a dual 4150 TB setup, sitting on top of a 12-71 blower in a Chevy Caprice SS cop car (2013) Injectors are on TOP of the rotors. It started and wants to idle at 3000-4000 rpm, timing way retarded because its above commanded idle rpm, headers glowing etc, but it didnt want to lower TPS below 26% or so to drop idle for soem reason. After asking if theyve eliminated all vac leaks for last month or so, we found brake booster wasnt on back of the manifold... so better now, will run at 1800.

Ive played around with idle scalar and not sure exactly how that should be set. Primaries open before secondaries, so 4 barrels idling. Surface area of that is slightly less than 90mm stock TB (9.62" vs 9.8" or so I think it was) Thing is how should it be set to accoutn for the other 4 barrels that open up with the progressive linkage? Want to get idle squared away first.

I wish you could log the actual math taking place, and see idle airflow being converter into blade area/tps. Why wont it chase the TPS any lower than 19% in the log? its at 1900 it knows its above commanded idle because timing is pulled to the min I set (I changed this from the - numbers allowed because it would backfire HORRIBLE) trying to get it down but it wont move blade any further shut?

Under Engine - Idle - Airflow, open up the "Idle Airflow Minimum" table.

Think of this table as an absolute minimum blade angle. The PCM uses the ETC Scalar to calculate a blade angle based on this table...it will never close below that calculation.

That said, I'd try to reduce the numbers in that table and see if you can get the blades to close more.

That's what I thought. But I put ridiculous low number in like .100 lb/min and still will idle at 1800 rpm, pull timing to minimum because it knows its above commanded idle, but not lower tps to bring idle down?

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Originally Posted by MikeOD

Under Engine - Idle - Airflow, open up the "Idle Airflow Minimum" table.

Think of this table as an absolute minimum blade angle. The PCM uses the ETC Scalar to calculate a blade angle based on this table...it will never close below that calculation.

That said, I'd try to reduce the numbers in that table and see if you can get the blades to close more.

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Try zeroing the Proportional and Integral Step values and set the Final Min Air table to all 64's. This will remove thse values from the equation and you should be able to control the blade TPS% with the Percent Max and Percent Max-Brake values. Once you get them set so the blade is opened to produce a good idle (defined as the timimg is hovering right around your commmanded idle timing) the re-inset the Proportional and Integral values, reduce by 50%, then interpolate the Integral values from the 0 value to the 512 and then from the 0 to the -512. Lastly set the entire Final min air table to say 10 and see where you are at. If idle timing is below the commanded then reduce the min idle air value, if above then increase the value. Blip the throttle and if return is very slow or not at all to idle rpm, then lower the Min idle air value. If returns too fast (1 sec) then increase. Also make sure you MAF and VE values are reasonably tuned.

Are you using the IAC blocking plate? Is this applicable to your setup?

Update -- Thinking while taking the dog for a walk...if you have 2 TB's and are controlling from 1 TPS signal, then the scalar needs to be half so IIRC the 5300 stock value should be changed to 2650 or so. Also make sure the TPS drive voltage is not having a problem driving the two TB's if that is how the setup is configured.

See if that helps

Ed M

Yes IAC blocked off

My belief is the g/sec values in the min airflow table are converted to a throttle position, though I don't know exactly how that's done. The computer then doesn't let the throttle blade close past that point.

I do not believe it actually looks at the airflow it's seeing from the maf/VE airflow data and adjusts how far open the throttle is to make it match the min airflow values.

My opinion is its a hard set limit that stops how far the blade will close (not really an automatic adjustment to try to achieve a particular airflow. It just figured out the min throttle position and doesn't let it close past that).

I've messed around with this some by engine braking and seeing how far it will close but haven't spent any time figuring out how it figures out the %'s yet. Probably not something I could figure out anyways.

Have you tried setting the whole table to 0 just to see what happens?

As I understand it (and have used), if you set the min air table to 64 and prop/integral tables to zero, it will take ithem out of play. At that point the amount the throttle plate will open or close is controlled by the Percent Max and Percent Max- braking parameters. The first is used for coastdown and the later is for stationary idle (worse case in auto in gear, ac on etc.). While they are a percent, they too are converted into an effective area then to a TPS%. I know of no "decoder ring" that shows that conversion but you can log the TPS% and move the percentage and you will see the blade (TPS% PID) increase and decrease. Using the base idle timing value, you can establish the "set point" for this value which represents the maximum the throttle blade will open (opposite of min idle air). When done, you normally add about .04 to .1 to handle cold starts as all the previous adjustments are made at operating temp. Once the Max is established you set the Min idle air (Final air) to a starting value (14 sh) and see how the car responds to throttle blips...too slow a recovery and the MIA is too high and too quick, its too low. The gol is to establish the 2 bvoundaries (mx/min) by which the Proportional and Integral air correction can operate between.

Ed M

With min air table set to 64 (or 8 in lb/min which I usually use) and PI tables 0d out, and Percent Max tables set at 3.6% it would idle at 38% TPS. I peeled it all the way down to .5% TPS, with the last percent or so having hardly no effect on the final outcome really. Go lower and it wouldnt stay running. So it would idle at 20% TPS 1800 rpm with target value of 1200 or so, but will not shut the blade. This is with a Min Airflow value off .76 G/S or .1 LB/MIN - a rediculously low value. It should have no min to hold it up correct? Effective Area Min Fail set to 1 from OEM value of 5 and OEM idles at 8-9% blade. It will not pull idle TPS down to get it to target

Ed I know you said scalar should be doubled, but I dont think it should be when its mathing for idle area control. It does have twice the blade area with two TBs, but for the first 30-40 % of throttle travel which is the area of concern we are working with, only half the butterflys are moving because it is a progressive linkage


Keep in mind, I bumped idle spark control to only pull out -2 degrees when over target, because it was making the headers glow something fierce.

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Originally Posted by GrannySShifting

With min air table set to 64 (or 8 in lb/min which I usually use) and PI tables 0d out, and Percent Max tables set at 3.6% it would idle at 38% TPS. I peeled it all the way down to .5% TPS, with the last percent or so having hardly no effect on the final outcome really. Go lower and it wouldnt stay running. So it would idle at 20% TPS 1800 rpm with target value of 1200 or so, but will not shut the blade. This is with a Min Airflow value off .76 G/S or .1 LB/MIN - a rediculously low value. It should have no min to hold it up correct? Effective Area Min Fail set to 1 from OEM value of 5 and OEM idles at 8-9% blade. It will not pull idle TPS down to get it to target

Ed I know you said scalar should be doubled, but I dont think it should be when its mathing for idle area control. It does have twice the blade area with two TBs, but for the first 30-40 % of throttle travel which is the area of concern we are working with, only half the butterflys are moving because it is a progressive linkage


Keep in mind, I bumped idle spark control to only pull out -2 degrees when over target, because it was making the headers glow something fierce.

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So let me understand this, With the two Percent Max values at 3.6%, the TPS% PID read 38%. Where was the avg timing value? When you get this right, the Over/under speed timing correction will stop imparting so much control. You then said "..peeled it back.." which I assume you mean you lowered the Pecent Max values to some percent very low which yielded a TPS% PID of .5% or did you lower the MAX Percent values to .5% which yielded a ?? TPS%?

"Go lower", go lower than what? and it wouldnt stay running (what were the TPS%PID values as you were lowering to the point of not running?

"So it would idle at 20% TPS..", what were the Percent MAx values at this point? You say the blade wouldn't shut....at any Percent max setting or it wouldn't shut any more than to the 20% TPS% PID value?

When you say half the butterflies, again I assume you mean 4 (the 2 primaries on each TB), is that correct? As far as scalar goes, if you used the 4 values to arrive at the total effective area than I believe you are correct. What also may need to be considered I would think, if the opening linearity of the standard TB (defined by the scalar) is proportional to your setup. In a DBC setup we can define the effective area by steps which would resolve that issue.

Now my head is really spinning :-)

Ed M

Welcome to my world! Haha i did not design this project i just inherited it. Two OEM TBs vertically facing with the readily available Oz harness would have made this a much easier task!

3.6% Percent Max = 38% final TPS, idle way high, idle timing at -8 degrees. Lowered P.M. values all the way to .5% to get @20% final TPS as shown in log and file I just posted. Set P.M. to .2% for example it wouldnt run though, even .4% seemed problematic, so back to .5% starts right up idles at 1750 or so as shown in log. ECU from that point on, even with proportional and integral stuff repopulated, will not lower the TPS from that 20% to get it idling at target value.

We did a test, unhooked motor from throttle shafts, held blade in place it would idle at 1400, and the TB would lower TPS to 12% or so? But something isnt physically limiting blade from shutting because we could get it idling lower by hand than it would connected to motor

Yes 2 primaries on each TB. i originally calced one TB blade area to be slightly less than a 90mm single blade TB

OK, may be seeing this a bit better now. The 18.8% with the Airflow Final Minimum set to 64 is its max and obviously in your setup is not a problem, its trying to get the blade to close more. Set the PM values to get you the 18.8%. To lower, the Final Min Airflow should do the trick. Set the entire table to .5 g/sec (you tried .76) and see if the TPS%/timing comes down. Leave the PI zero'd out for this test.

The Scalar value for a 102 mm TB is like 7300 or so. If you are saying 1 of the 8 bores is slightly less than 90mm (90mm*8=720mm) then the 4 bores in play with idle is (90mm*4) or about 360mm, three times the 102mm. There isn't enough range in the scalar to accurately tell the PCM what size TB its dealing with so it can calculate a low enough TPS% from the effective area (developed from the g/sec requirement) or EA*%/EA ...Your min idle air values will have to be miniscule to compensate.....

Unless I am missing something.....

Ed M

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Originally Posted by mowton

OK, may be seeing this a bit better now.

The Scalar value for a 102 mm TB is like 7300 or so. If you are saying 1 of the8 bores is slightly less than 90mm (90mm*8=720mm) then the 4 bores in play withidle is (90mm*4) or about 360mm, three times the 102mm. There isn't enoughrange in the scalar to accurately tell the PCM what size TB its dealing with soit can calculate a low enough TPS% from the effective area (developed from theg/sec requirement) or EA*%/EA ...Your min idle air values will have to be minisculeto compensate.....

Unless I am missing something.....

Ed M

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4 round 1.72" bores in play at idle. Pure math ends up 6000, but ratio of area of those compared to 102mm (math says 8167 there but minus throttle shaft area about 89%=7300) gets me a 5336 with same 89%. The factory 90mm TB area in mm x.89 is @5600 which is what factory program had. Math says slightly smaller than stock. So close you could leave it stock, and bake the error into the other values, or at least it should LOL

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Originally Posted by GrannySShifting

4 round 1.72" bores in play at idle. Pure math ends up 6000, but ratio of area of those compared to 102mm (math says 8167 there but minus throttle shaft area about 89%=7300) gets me a 5336 with same 89%. The factory 90mm TB area in mm x.89 is @5600 which is what factory program had. Math says slightly smaller than stock. So close you could leave it stock, and bake the error into the other values, or at least it should LOL

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Wow, that was a senior moment for me....sorry, should have checked the math because I thought you said each bore was equal to a 90mm TB opening. Yes so with the 4 bores (1.72"/43.7mm each) equal to 5808 and accounting for the 4 shafts, you are just about at a total of 1 ls2 90mm TB so the 5600 should work as you have in the latest tune file.

Now I still don't know why you can't get the Throttle blade to close more than 20% as I see the results above were based on the tune file with the 56xx scalar amd .76 g/sec in the Final Air table.....Is there an adjustment on the TPS/throttle blade motor? Accufab has one for theirs. You are commanding 6% yet seeing 20%? I am not really experienced with these TB's

Ed M

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Originally Posted by mowton

Wow, that was a senior moment for me....sorry, should have checked the math because I thought you said each bore was equal to a 90mm TB opening. Yes so with the 4 bores (1.72"/43.7mm each) equal to 5808 and accounting for the 4 shafts, you are just about at a total of 1 ls2 90mm TB so the 5600 should work as you have in the latest tune file.

Now I still don't know why you can't get the Throttle blade to close more than 20% as I see the results above were based on the tune file with the 56xx scalar amd .76 g/sec in the Final Air table.....Is there an adjustment on the TPS/throttle blade motor? Accufab has one for theirs. You are commanding 6% yet seeing 20%? I am not really experienced with these TB's

Ed M

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Adjustment on TB motor?its a OEM motor driving a shaft with linkage to the two TBs

This thing is not fun

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Originally Posted by GrannySShifting

Adjustment on TB motor?its a OEM motor driving a shaft with linkage to the two TBs

This thing is not fun

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Custom or aftermarket? Who makes it? I think, based what I know, this is where your problem lies.....any pic's of the setup?

Ed M

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Originally Posted by mowton

Custom or aftermarket? Who makes it? I think, based what I know, this is where your problem lies.....any pic's of the setup?

Ed M

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Attachment 55199


Attachment 55200

What in the hell, lol

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Originally Posted by schpenxel

What in the hell, lol

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Yes, welcome to my nightmare!

With that tie linkage it looks like the perfect candidate for an ECU swap and a drive by wire change. LOL

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Originally Posted by wetcoast

With that tie linkage it looks like the perfect candidate for an ECU swap and a drive by wire change. LOL

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Not when its a 2014 Caprice PPV cop car and you have to interface the rest of the car :/