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Message: <blockquote data-quote="rz5.0" data-source="post: 1219876" data-attributes="member: 12700">once you have the idle stable it would be ideal to get the iscdc between 25% to 35%, reason being is that it will allow headroom for cold enrichment, if its below 25% then close the throttle body stop (reduce air), if its above 35% you need to open the throttle body stop (increase air) It is imperative that the above be followed, if the ISCDC is below approximately 20% then the IAC valve is completely closed and the ECU cannot control the idle. now with a stable AIR MASS or MAF value and ISCDC we can input the correct info we need to let the ecu know how to control idle correctly go to the neutral idle air function FN875N and put in the NUBASE value and the actual AM value you averaged, if you only have MAF to log then you'll need to convert from kg/hr to lbs/min by multiplying the average MAF value by 2.2 then dividing by 60 ex: your average MAF at idle was 28 kg/hr, 28*2.2/60= 1.026 lbs/min, not exact but good enough, this value goes directly into the idle air function next you'll need to dial in the throttle body airflow scalar ITHBMA, the t/b airflow scalar is the amount of airflow the ecu can not control you can figure out how much air was coming through the tb blade by looking up the isc transfer table [COLOR=#16545]FN8000[/COLOR] for newer ecu's or the transfer function fn800 for the older ecu's calculate the lb/min contribution from the isc (known as DEBYMA) by interpolating the flow at your logged ISCDC value if you can log the DEBYMA payload then you don't have to do the following, since most def's do not have access to that payload we will calculate the isc airflow the long way ex: average ISCDC was 35, lookup your isc transfer, for this example, the transfer gives: 39 dc = .25 lb/min and 28 dc = .12 lb/min so to interpolate what the flow is at 35dc, 39dc - 28dc = 11 dc difference; now work the flow .25 - .12 = .13 difference; .13 airflow difference over the 11 duty cycle difference gives us: .13 / 11 = .0118 per duty cycle now we subtract our dc from the upper end of the scaling 39-35 = 4; we now multiply our duty cycle difference by the airflow per duty cycle 4 * .0118 = .0472; not done yet, dont forget to subtract this from the upper airflow value of the airflow scaling from which you interpolated your iscdc to get the total isc airflow .25 - .0472 = .2028 the isc valve is flowing .2028 lbs/min of air at 35% dc see how simple it is, just basic math, the ecu uses the following formula AM - DEBYMA = ITHBMA now subtract that value from the AM, ex: 1.026-.2028=.8232 this is the value for the throttle body airflow ITHBMA scalar, as you can see this is the amount of air the ecu SUBTRACTS from the AM to calculate the iscdc it needs to get to the rpmdsd before continuing its imperative that you fully understand this statement, to clarify in other words, the ecu looks up the idle air function to calculate how much airflow AM is needed to reach a dsdrpm, by knowing what the actual AM from the maf sensor and the amount of airflow that is going through the throttle body ITHBMA it can very simply calculate the duty cycle needed of the isc valve (a.k.a. Idle Air Control valve) to get the amount of air mass to reach a specific dsdrpm you should be able to infer by now that fn875n - ithbma = isc flow (lookup dc from fn8000) AM (maf) - fn875n = ipsibr (correction) since this can be a bit confusing i will do another example, lets say the engine has an average idle MAF of 32.32 which equals 32.32 * 2.2 / 60 = 1.185 AM at an iscdc of 17.5%, by looking in the function fn800 or fn8000 we can get the scaling values, A9L2 has the following values: .12 lbs/min = 28dc 0 lbs/min = 10dc which gives us 28-10=18 dc difference.12-0 = .12 airflow difference.12/18=.0066 per dc now to interpolate the airflow 28dc - 17.5dc = 10.5 dc * .0066 = .0693 .12 - .0693 = .0507 lbs/min flowing through the idle air control valve when the duty cycle is at 17.5% am - isc air flow = ithbma 1.185 - .0507 = 1.1343 be sure you understand this before proceeding!!! when an engine is cold it will require more rpms to stabilize, thus we need to have a higher rpm value with airflow for the ecu to interpolate between for the increased engine speed to do this, increase the NUBASE scalar by 500 rpm, once the engine has stabilized at the new dsdrpm calculate the new average AM then insert that value and the new dsdrpm value into the FN875N function just like you did before NOTE: EVERY FUNCTION IN THE ECU MUST BE SCALED TO THE ABSOLUTES, THIS MEANS THE TOP MOST VALUE MUST BE THE HIGHEST POSSIBLE INPUT THE ECU ALLOWS AND THE BOTTOM MOST VALUE MUST BE THE ABSOLUTE LOWEST VALUE THE ECU CAN CALCULATE, THIS APPLYS TO ALL FUNCTIONS AND ALL YEAR ECU'S </blockquote>