[Diy_efi] idle control 1227747

[Bret Levandowski]

Iac steps vs coolant is extra air for higher idle on cold start. At 56 deg C and higher you should have no more than 24 counts on the table. (this will actually vary motor to motor and should be slightly less for yours) The motor build/size dictates counts below that temp. This table will have some effect on idle. You want to use the target idle RPM vs coolant temp table. Set your desired idle in this table. If you're still idling too high and IAC counts are too high, check your ECM constants table and make sure that the % TPS to enable open loop idle is at least 1% higher than your ACTUAL TPS reading at idle, otherwise it's trying to idle in CL. ( which from what I've been told is a no - no) Make sure your 'base idle is set correct. Unplug and remove the IAC. Fully extend the pintle and re-install it in the TB (I'll save everyone the trouble...I'VE NEVER SEEN THIS DAMAGE AN IAC) I've had people chastise me for this before ;p  Anyhooo... Be sure to warm up the vehicle before starting
 this procedure. After installation, don't plug the IAC in. Start the vehicle and monitor the idle. It should be set around 500 rpm (depending on cam specs) with TPS anywhere from .4v to .7v. Shut it off, plug in IAC re-start and hopefully you're at target idle. If not....      Ski

Darryl M Gilbert <dgilbert78 at juno.com> wrote:  Hello: 1227747 355cu in SB Chevy. Trying to figure out how to get idle
down to the idle speeds in the target idle vs coolant table. Currently
ECM wants to keep the engine running approx 1100 RPM, with 80 IAC steps.
Temp is at 171 deg F. TPS reading .51 volts at idle, but Idle speed will
not come down to target idle table speeds?? Is there a switch that tells
the ECM when to invoke the target idle table?? I think IAC steps vs
Coolant is for Fast Idle when cold?/ Any help will be greatly appreciated
Darryl..
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