Car idles like crap when A/C is on

[JamesFoster]

Hey guys, quick question. My car idles great when the A/C is off, but when I have it on the revs tend to drop down around 500-600rpm it runs kinda rough. Any ideas?

 

[beaner]

Voltage changes when you introduce a load to the engine, causing a lean condition and change in idle. I see you have 'link 2.5. 3.0 lets you offset this. click

edit: Try to post a log of it happening.

 

[JamesFoster]

Oh I don't have link on the VR4, sorry didn't specify, and the voltage does drop to around 12.8-13v when it happens.

 

[beaner]

Well, the ISC should compensate. It won't be instant, but that's pretty much the purpose of the ISC. Do you have one?

 

[JamesFoster]

Yes I do. I checked the ohms and they're within spec but I haven't applied voltage to it yet. I'll have to do that to see if its working.

 

[desant78]

Maybe some more info....battery in stock location? And idles.great means 750rpm?

 

[jepherz]

Should idle at 850 rpm.

 

[JamesFoster]

Battery is in the back, and the idle varies between 850-950 when it's idling good. I'm wondering if I should replace the isc, or maybe the TB needs to be rebuilt?