LT1 Idle Bump For A/C - LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums
 
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post #1 of 3 (permalink) Old 10-15-2017, 10:57 PM Thread Starter
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LT1 Idle Bump For A/C

Can anyone tell me how this works? I have a '94 swapped into my C-10 peekup. When I flip the A/C on the idle dips to a stall unless I play with the accelerator. Want to know what I have to hook up so the ECM will do this.

Steve
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post #2 of 3 (permalink) Old 10-16-2017, 07:58 AM
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The idle increase is controled by the pcm. When you flip the a/c on the pcm commands the IAC ( idle air control) to open up the air bypass passageway more. The idle now compensates for the extra drag of the compressor.

You need to download the 94 service manual at the following link. It will have the pcm wiring diagram, and pcm chart of what each wire does and where it goes. This will be in the driveability & emissions section. Wiring section will have complete wiring diagrams. www.mediafire.com/?40mfgeoe4ctti

Note in manual that a/c sensors and control head in car, send info to pcm on a/c status. I believe it's the control head, when you switch on a/c that tells pcm to open up iac more. This is what kicks the idle up.

If you have the aldl from lt1 wiring installed, & have a scanner that does real time sensor data, you can monitor the "a/c request data stream to see if pcm is commanding a/c to go on. Also monitor iac counts.

Last edited by cocobolo95; 10-16-2017 at 08:04 AM.
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post #3 of 3 (permalink) Old 10-16-2017, 10:57 PM Thread Starter
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Thank you very much cocobolo95. Just the info I needed. I used a Howell Ent. harness & reflashed PCM on this swap and it works great but my (poor) memory seems to think that it used to kick the idle up fine, but this summer it didn't. We'll see what I find.

Steve
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