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Old 07-03-2014, 11:28 AM
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Tinkerjeep Tinkerjeep is offline
Join Date: Mar 01, 2009
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Originally Posted by Jeepdawg
Well, I found that the problem was the minimum idle screw was screwed too far in which was preventing the throttle plates from closing enough to cover the ported vacuum holes in the venturi.

By backing off the min idle screw I can get the vacuum down to 0 in, but the idle is too low there. At 1-2" of ported vacuum I can get an idle of 830 rpm in N.

But now I have a new issue. The idle surges a bit in N but is steady in D. It seems to steady out a bit putting a load on the engine.


Originally Posted by Tinkerjeep
Under normal circumstance the ported vac signal should not be present at idle. Your throttle blades are open or your idle is too high.

AHA! So I'm not smoking crack.

Glad you got it figured out/ fixed.
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Old 07-03-2014, 05:23 PM
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Jeepdawg Jeepdawg is offline
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Join Date: Jun 09, 2003
Location: SF Bay Area, CA
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I have never owned a car with throttle body EFI, so I didn't realize there was an idle stop screw like a carb.

The Howell setup looked very nicely installed so I **presumed** that whoever installed it knew what they were doing.

But, the PO had all the vacuum hoses wrong. Namely he had the PCV port on the throttle body connected to the intake manifold instead of the PCV valve and purge canister. In order to make get enough air to idle he had to open the throttle butterflies which closed off the ported vacuum.

And, you can't just adjust the screw to set the idle. There is a whole setup operation involving resetting the EFI brain which I need to do once I get the time.
1974 J20 Pioneer, ZZ/8,000 GVW, 401-4V, QT.
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