How to check for vacuum leak and Idle air control valve -
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Unread 01-05-2015, 05:12 AM   #1
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1992 YJ Wrangler 
Join Date: Apr 2014
Location: Salt Lake City, Utah
Posts: 4
How to check for vacuum leak and Idle air control valve

So my jeep has a very rough idle at start, where it will surge and then drop low to the point of the engine dying. Then when starting to drive, the engine will jerk and stutter. I've read on here that it could be a vacuum leak, fuel pump, or idle air control valve. My problem is A) I don't know how to test for vacuum leaks B) I don't know where the IAC is. Any help would be appreciated.

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Unread 01-05-2015, 05:34 AM   #2
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1992 YJ Wrangler 
Join Date: Dec 2012
Location: The Desert, Nv
Posts: 1,892
I use an unlit propane torch around vacuum connections at idle. Follow the vac hoses for cracks or splits that are tough to see. Run it around the air intakes. (Throttle body and intake manifold)
If there's a leak, the idle will smooth out or raise up. Don't forget about the CAD vac lines.

People use carb cleaner the same way. I don't because it's flammable. If you use carb cleaner, have a fire extinguisher handy. carb cleaner works well and it's normally safe.
What happens in my Jeep, stays in my Jeep
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