How do I test my IAC?

[SamBone02X]

I’ve been trying to chase down this weird low/rough idle issue for the past 2 months or so and I have checked everything else that could possibly cause this (except fuel pump) and everything checks out. Plugs look great, TPS has been replaced recently, IAC/TB has been cleaned several times (TB is also new). I’ve got nothing other than trying to test the IAC, which I’d like to know for sure before spending $120 on a new one. Thanks!

 

[Jerry Bransford]

Are you removing the IAC to clean it or are you spraying a throttle body cleaner into the throttle body at idle rpms?

 

[SamBone02X]

I

Are you removing the IAC to clean it or are you spraying a throttle body cleaner into the throttle body at idle rpms?

Hey Jerry, I sprayed it in at idle per your instructions on another thread I read a while ago. Would it help to take it off and clean it?

 

[Jerry Bransford]

I

Hey Jerry, I sprayed it in at idle per your instructions on another thread I read a while ago. Would it help to take it off and clean it?

No, you're cleaning it in the way that will get the entire IAC air passageway clean.

 

[SamBone02X]

No, you're cleaning it in a way that will get the entire IAC air passageway clean.

I’m fairly lost as to what else could cause this, it has to be the dang IAC, the tach moves around at idle and I know the IAC controls most of the idle. Do you know how to test it?

 

[Fulton_Hogan]

What about the main vacuum connection off the engine? If you have a 4.0 it's on the driver's side of the engine, just under the plastic rail at the top edge. Is it present but loose or deteriorating? It can cause errant idle conditions.

 

[SamBone02X]

What about the main vacuum connection off the engine? If you have a 4.0 it's on the driver's side of the engine, just under the plastic rail at the top edge. Is it present but loose or deteriorating? It can cause errant idle conditions.

Thanks for the idea, I will definitely check this. Where exactly is it? Under what plastic rail?

 

[Fulton_Hogan]

I have a picture of the spot in this thread I started when I happened to find mine was falling apart at the touch. It's not a great photo, so look between the braking system components and the engine. There's a thin black hose, which if you trace it you'll find where it attaches to the intake manifold.

https://wranglertjforum.com/threads/deteriorating-vacuum-harness-elbow.52367/#post-926816
My understanding is if the vacuum system begins to leak, the computer can see it, and maybe compensate for it, but only so much. When it can no longer adjust things properly, your idle can begin to go wonky. Worth checking out.

 

[SamBone02X]

I have a picture of the spot in this thread I started when I happened to find mine was falling apart at the touch. It's not a great photo, so look between the braking system components and the engine. There's a thin black hose, which if you trace it you'll find where it attaches to the intake manifold.

https://wranglertjforum.com/threads/deteriorating-vacuum-harness-elbow.52367/#post-926816
My understanding is if the vacuum system begins to leak, the computer can see it, and maybe compensate for it, but only so much. When it can no longer adjust things properly, your idle can begin to go wonky. Worth checking out.

Will Definitely check it out, thanks!