[Gmecm] IAC control??

[David Haggard]

Here's a possibility. 

If you have changed the "IAC steps vs. Coolant temp" table (controls cold-engine IAC settings), there is another couple of settings that can make it "hang" or speed up. I had this same issue myself, and found the answer.

If you have lowered the settings in that table, then you might also need to lower the "Kickdown steps."

>From the document "747 IAC Control"--
<quote>
	0x5D7: Kickdown delay timer value (seconds).
	0x5D8: Kickdown steps.

	These two together form a post-startup rpm reduction. 
	The kickdown delay timer starts right after startup. 
	Once the timer has expired, the IAC is extended by
	the amount of kickdown steps.

	A nuance: The kickdown steps must be less than the
	steps used in the IAC position vs. coolant table
	value (0x5F5): Otherwise kickup will occur. The 
	kickdown steps are subtracted from the IAC position
	steps, and are added to a term that is decayed out.
<end quote>

When in diagnostic mode, I think these settings are ignored, and would allow normal operation.

> -----Original Message-----
> From: gmecm-bounces at diy-efi.org 
> [mailto:gmecm-bounces at diy-efi.org] On Behalf Of Cowen
> Sent: Thursday, June 09, 2005 7:42 PM
> To: gmecm at diy-efi.org
> Subject: [Gmecm] IAC control??
> 
> Hello! I'm trying to trouble shoot a 1988 Pontiac 2.8l with a 
> '727.  Problem is, the IAC retracts the pintle for starting, 
> and then (intermittently) doesn't extend again.  Then the car 
> idles at 2000 RPM. This car is not pulling any codes - I 
> checked a few times, and I just get a reassuring "12". 
>   If I put the ECM into diagnostic mode, the pintle extends 
> just fine, every time (so the IAC seems to be OK).  If I 
> extend the pintle, leave the IAC disconnected, then start the 
> car, and finally reconnect the IAC with the car running, it 
> runs perfectly.  It even compensates for power steering load.  
> Question is, what inputs does the ECM need to set idle?  
> Coolant temperature, power steering pressure, and what else?  
> Other notes:  the battery is crap, does the '727 increase 
> idle speed when Bat Voltage is low? Also, the temperature 
> GUAGE works fine, but the temp indicator light is always on.  
> If the ECM uses the same
> (faulty?) sender as the indicator light, shouldn't it pull a code?
> Thanks for any suggestions!
> 
> 
> 
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