Poor idle control with AC on

[Al Pizzica]

Hi, all, I've had increasingly poor idle control when the AC is on over the last year.
With AC off the engine purrs at 800rpm but with it on, and especially at a stop, the engine waxes and wanes between 1100 and 900 like a constant thrumming at about 30-45 times per minute. There is also a very, very slight off idle hesitation that I attribute to the tranny when pulling out from a stop but thought worth mentioning here.
There was only one other post on this forum I could find but it seems unrelated to this specific issue (that guy had injector problems).
Does the LR4 have an idle air controller? This seems to be a culprit in other makes and models. Maybe vacuum leak? Anyone else with this issue?
2013 LR4 106k miles.

 

[djkaosone]

There is an IAC on the back side of the intake manifold towards the firewall. There's a possibility that one of the vacuum hoses is leaking.

 

[Al Pizzica]

Thank you for that tip, no wonder I couldn't find it in the front.
Any clue if these two empty connectors on the front are part of the problem? Should these be like this?

 

[djkaosone]

Those connectors are blanked off on purpose. The older version of these coolant hoses were routed different.

 

[Al Pizzica]

It's a rats nest behind the intake manifold. I can see the vacuum lines but not manipulate them even when I unbolt the wiring harness.
Does anyone know of a tutorial for moving it? Maybe as part of the rear crossover replacement?

 

[djkaosone]

You'll need to remove the throttle body, fuelrail cross pipe, unplug harness for iac and map sensors, and bolts holding the intake manifold. Once the intake manifold is removed, you'll see the iac attached to it.

 

[Al Pizzica]

Boy, I was hoping to just get back there behind it but I can see how that is probably much easier. Thank you.

 

[ryanjl]

Any way to do a smoke test on these engines to spot a vacuum leak before you go through all the trouble of removing all that stuff?

 

[Rover Range]

There's no IAC on the LR4.
The vacuum motors on the rear of the intake are for the air diverter valves within the intake. Doesn't affect the idle.

 

[Al Pizzica]

There's no IAC on the LR4.
The vacuum motors on the rear of the intake are for the air diverter valves within the intake. Doesn't affect the idle.

So you think it's an electronic or throttle body issue? Maybe an electrical issue if the AC is drawing a lot of amps? Alternator? The battery is also getting old and I know an old battery in a landy causes mystical and bizarre issues sometimes.