LS stalls when AC turns on
 

Wondering if anybody has come across this issue. Did an LS swap on my 69 camaro and when I kick the Vintage Air AC on the idle doesn’t bump up and it stalls. Any tips that can remedy this would be greatly appreciated.
Thanks
Steve

Seems like the IAC is either improperly set so it's so far open just to hold a normal idle there's nothing left when you add the load with A/C. Or it isn't working at all. Need to see what the IAC counts are at idle with no A/C and fully warmed up. You want the IAC to be mostly closed down at a warm idle so it can open further and bump the idle speed when the engine gets a load like A/C. Usually and IAC count of 20-40 at a warm idle and no load is in the range. If the IAC is at 160+ it's pretty much all open and can't do anything.

If it's too high you will have to bump the idle screw on the throttle body until you can maintain a hot idle desired speed, and the IAC can close down so it'll actually function when you need it. If it's DBW then ignore everything I just typed lol.

The bump up has to be tuned into the ecu, especially if its not a factory ecu. They sometimes provide a pigtail, but its not always turned on in the ecu. You can also over charge the ac system and put enough load on the compressor to kill the motor as well. Also make sure you have a large enough alternator to handle the amp spike when the fans kick on. That can also cause accessory load issues as several of the front drive kits out there only come with 140 amp alternator or less and that won't cut it.

Jody Im gonna grab my scanner and check when i get home and see what the IAC is doing. OH and yes its a drive by cable.
Thanks

Mike Im gonna check the pressures for sure..... good point! Also gonna load test my alternator and see whats going on? Im running a factory corvette alternator as well as the accesory drive.
Thanks guys!

Steve please let us know once you fix this issue.
I am having exact set up as yours with OEM PCM and Cammed LS6.
The engine stalls and dies if I rev it when the vintage air AC is on. This happens when the AC clutch is engaged.

The rpm drops below the desired rpm and stalls. In fact, sometimes when letting off the throttle and pressing the clutch to come to a stop, the rpm drops and engine dies even before coming to a dead stop

Yes for sure I will post my results. So far I have swapped out my corvette alternator for a 2008 I believe Chevy equinox 140 amp alternator but haven’t checked my IAC counts as my scanner won’t do that. Gonna pick up a new scanner and see what happens. I will post my results soon. Thanks everyone
🍻

If the IAC settings and base idle screw are adjusted correctly I would look at the Throttle follower tables. I've had this issue myself and adjusting the throttle follower tables allowed me to slow down the rate the throttle drops and eliminate the overshoot on a snap closing of the throttle blades.

Thanks Jody for the input.

My IAC counts at operating temperature are around 59 or so. I have read the recommended counts for cammed engines should be between 40-60, so I am within range I guess.

I have looked at the throttle follower decay/ delay rates, and the column axis was for vehicle speed not rpm.

So I was not sure what needs to be adjusted. Because the issue I am having is at idle and while driving.

I have seen some videos in youtube where they recommend to increase the timing from 0 to 400 rpm at spark tables( in park & drive) to be at 30 degrees as this would work as stall saver.

I have just changed the timing but need to write the changes into my pcm and see how it goes

Did you ever resolve this?

What scanner/software package are you using?

I have a 72 el camino with a 2002 5.3L from a chevy Silverado. It has a 1998 camaro cam and intake manifold with 2002 LS6 camaro injectors. It sometimes stalls when coming to a stop.

thanks

I’m still struggling with it. My IAC counts are up around 130 at idle warm. ☹️☹️

What computer is it and what tuning software are you using?

I’m using the stock 2000 camaro red and blue plug computer. Tuning software I have no idea. I had the car tuned on the Dyno by a shop near me.

So is the tuner making any changes to the tune, throttle follower tables, idle timing, etc? The tune is going to have to be tweaked to fix this. I would get the idle set when fully warmed up to have the IAC closed down to 40 counts or so with no idle timing additions (too high right now at 130 warmed up), slow down the follower table, then bump the timing at idle to 30 degrees or so and allow the idle timing changes to stabilize the idle speed (some tunes shut this off and I've found it helps a lot on mine).

By the way, your tuner should know all this, if not switch tuners to someone like Mike Norris. Guarantee he'd figure it out, but you'd need someone with the correct software to load his tune since you don't have the tuning software yourself.

He told me it’s as good as it’s gonna get. He said the intake I have on it makes no torque at idle.

Find another tuner...

Maybe I missed it but the ECM whether GM, Holley, ect needs to be told the AC is on. Most swaps we see the ECM has no communication with the AC system. If you look at Stielow's builds he adds a GM pressure switch to the Vintage Air plumbing. This allows the ECM to reference the "AC on" rpm tables. If the ECM doesn't know that the AC is on there is nothing a tuner can do for you aside from bumping the base rpm tables to a point the vehicle won't stall.

We figured it out. We Added a few wires to the ecm that we found on LS1 Tech so it knows the AC was commanded and now new tables are introduced and the ECM bumps up the idle. Works soooooo much better. Thanks everyone for the help 👍

Steve, glad you got it sorted out.
I am having the same ECU as your (red & blue ) connectors with vintage air.
Could you please share with us what wires ( pin numbers) you added on which connectors to bump up the idle when AC is on, and how you got them wired up to AC compressor.

Also, do you have the Vintage air binary, trinary switch from VA or you are using LS1 pressure switch.