EFIDynoTuning Forum

Symptoms: racing idle after executing a start, then sometimes surging before settling down to a “normal” idle speed. During low vehicle speed tip in’s, rpms hang for awhile before rapid fall off. With the A/C adder this magnifies this behavior and car basically accelerates on its own with a/c on. On tip in off of idle speed from stops there is almost like a momentary fall off in rpm (delay) before rapidly accelerating. I haven’t made any changes to the calibration related to the Idle speed control or any spark adjustments. I have a new IAC, factory marauder throttle body on the cobra Eaton s/c setup. At warm stable idle ISCDTY is approximately 0.45 and DESMAF is negative at approximately -0.28. Engine speed is approx 650 rpm. SPK actual is approx 15-20. Engine stalls when unplugging IAC valve. Something seems off. What’s the recommended process? I’ve read that a desired target for IAC duty cycle is 25%. Do I need to perform the mechanical throttle control mod in this case?

you need to set the throttle stop correctly, obviously it needs to be opened a touch

then dial in the isc multiplier table and then dashpot

I performed adjustment to the throttle blade stop and have it idling with an ISC duty cycle of 0.25. I will read the write up and work on dialing the multiplier and then dashpot in. Thanks

yep np

Should I just remove about .15 from the values in the cells in the ISC multiplier table and see how it responds? What’s the recommended method for correcting the ISC multiplier function?

no you first have to get the throttle body set correctly then adjust the isc multiplier table to keep the idle air correction as close to 0 as you can.

Update: I set the throttle blade correctly. Then I had so make some changes to the mas air adders for a/c as fords values were bunk. I got it running more seamlessly during those compressor clutch engagements. I’m starting to understand how some stock functions were “calibrated” so inadequately.