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Message: <blockquote data-quote="rz5.0" data-source="post: 1219874" data-attributes="member: 12700">Idle Air 101 by Michael Decipha Ponthieux Last updated: 8-22-2013[COLOR=#16545]Note: all writing in this color does not apply to older ford ecu's (such as the foxbody ecu)[/COLOR] Idle Air Controlthe idle air neutral function FN875N and drive air function FN875D contain the actual air mass needed to reach a desired rpm WHEN THE ENGINE IS AT STABILIZED WARM IDLE ONLY and the isc table multiplier FN1862N cell(s) in use is at 1 before continuing be sure you fully understand this statement the idle air neutral function FN875N and drive air function FN875D contain the actual air mass needed to reach a desired rpm WHEN THE ENGINE IS AT STABILIZED WARM IDLE ONLY and the isc table multiplier FN1862N cell(s) in use is at 1 these functions are only dialed in ONLY WHEN THE ENGINE IS AT STABILIZED WARM IDLE (typically 200-220 degrees ECT), which means the engine has been running at least 15 minutes and the throttle has been closed for at least 2 minutes, and the FAN HAS BEEN OFF for at least 2 minutes ***you can not dial in idle air when the fan is on due to the extra loading!!! there is seperate values for that [COLOR=#16545]FN885 & FN822B[/COLOR] now you can ONLY dial in idle air AFTER your idle fuel is dialed in, if your in closed loop at idle your fuel kams should be near 1, if your kams are more than 5% off at warm idle you need to dial your idle fuel in first. YOU CAN NOT ADJUST IDLE AIR WHEN IDLE FUEL IS NOT CORRECT!! this is because any correction to idle fuel will alter the idle air requirements now ASSUMING you've got your idle fuel dialed in, get her up to WARM operating temp and stabilized idle, again FANS OFF <hr />make sure your average rpm is within 50ish rpm of demanded idle which will be the scalar NUBASE when in neutral, be sure there is no rpm adders in effect (such as fn825b ACT adder, fn825a ECT adder, fn821a voltage adder, fn880 time adder, fn890 bp adder) you can verify there is no adders in use by logging the payload DSDRPM, dsdrpm is the rpm the ecu is trying to target, with no adders in neutral DSDRPM will be the same as NUBASE, +/- 8 rpm due to it being two different memory structures the tps at idle closed throttle means nothing so long as its between the TAPMIN (tps minimum) and TAPMAX (tps maximum) if the tps is not within that range then the logged tps value will be the value of the scalar RATIV (failed tps value) verify the tps does not match RATIV at closed throttle, if it does then more than likely the tps value is too low, to fix this you can simple reduce the min tp scalars VTAP1, VTAP3, TAPMIN, to put the tps sensor back in range, i usually set all 3 of those scalars to 0.4 volts (82 adcts) folks used to believe the tps had to be at .99 for max power, thats complete crap anyone feeds you that garbage you punch them in the mouth as per decipha, the ecu takes the lowest tp voltage it gets and uses that as 0 relative position which can be logged as the payload TP_REL, this is known as ratch now with the engine at stabilized warm idle with no adders and no fan, keep an eye on the payload AM air mass value if you do not have access to the air mass payload than keep an eye on the MAF payload, if you don't have access to maf you'll need to log the maf voltage (imaf, mafv, or vmaf) then go calculate the air mass from it, if you can't log maf voltage, you'll need to probe the maf sensor and subtract approx .14 volts from it then go look up that voltage in your maf transfer FN036 to know the air mass in any case, you want to get an average, it doesn't need to be exact just a good guesstimate average, if its jumping around quite a bit then chances are your getting a bit of turbulence through your maf and it would be wise to install a mesh screen to smoothen out the airflow, prior to installing a screen you can try 'clocking' the maf by loosening the clamp and 'turning' it until you get THE HIGHEST POSSIBLE MAF at idle which should be where its most stable, IE... not jumping around alot, a .03 fluctuation is about normal log the iscdc as well or the "ISC duty cycle", you'll need this value to get the correct throttle body airflow value ITHBMA the isc duty cycle should be pretty consistent, [COLOR=#16545]if its not you need to tame your idle by increasing the idle air correction constants scalars TC_OVER and TC_UNDER temporarily setting the SPK_FBS_GAIN (feedback spark gain) value to 0 so that the ecu doesn't throw around spark at idle, keep in mind on a large lift cam or a stupid overlap cam setting the gain multiplier to 0 will probably make it surge, if this is the case you will need to increase the gain, a value of 1 usually works out well for most engines[/COLOR] if that still doesn't stabilize the iscdc you may need to disable idle air kam correction by either setting both the min correction PSIBRN scalar to 0 as well as the max PSIBRM scalar to 0 or if you have access to the isc global multiplier scalar IDCMUL set it to 0 and global isc adder scalar IDCOFS set to 35, if you had to set both correction clips to 0 and still can't get the idle to stabilize then you can temporarily clip the isc min duty cycle by increasing the DEBYCP scalar, keep increasing it until the idle is stableNote: for those with really stupid cams, you may need to permanently keep these correction scalars to 0 for a stable idle, if idle air is dialed in then you won't need correction anyway under most conditions, or you could possibly reduce the correction limits PSIBRN and PSIBRM, values of .05 and -.05 usually work out pretty well for most engines with stupid cams and still allows it to adapt to air changes</blockquote>