# 85 720 stuck on high idle



## dave2006 (Feb 14, 2015)

my 84 720 truck with the z24 motor it has the original carb that was rebuilt about a year and a half ago is stuck on high idle 2500-3000 rpm what can cause this


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## jp2code (Jun 2, 2011)

Does the 1984 have any electronics on it?

If not, the carb should have an idle screw.


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## dave2006 (Feb 14, 2015)

it has 3 sets of wires going to it and its not the idle screw I was driving and it was running good then when i came to a light it wouldnt idle down and i miss typed its a early 86 720 the late 86 is the hard body its 2wd 5 speed


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## dave2006 (Feb 14, 2015)

it has the z24 4 piston motor


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## jp2code (Jun 2, 2011)

Hi Idle is usually the Air Flow Meter (EF & EC-150) or the Idle Switch (EF & EC-174).

Right-Click the link below, select Save As, and save it to your My Documents folder:

d21_truck_1989.pdf

It is for the 1989, but it should be identical to your 1986.

The *ENGINE FUEL & EMISSION CONTROL SYSTEM (EF&EC)* is what you need to turn to.

You should start by reading the DIAGNOSTIC PROCEDURE (EF & EC-41) then attempt the SELF-DIAGNOSIS (EF &EC-71).

If you flip through those sections, you will see that #11 on EF & EC-45 is about Abnormal idling - high idle (after warm-up).

There is a big checklist of simple things to look for.


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## dave2006 (Feb 14, 2015)

i found that the diaphragm on the back of the carb was sticking now im seeing if I can get it to stay free or I need to replace it


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## jp2code (Jun 2, 2011)

dave2006 said:


> i found that the diaphragm on the back of the carb was sticking now im seeing if I can get it to stay free or I need to replace it


Yours has a carb? I thought all Hardbody trucks came with fuel injection. If yours does not have a throttle body on it, then it has been swapped out.


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## dave2006 (Feb 14, 2015)

It's a early 86 still a 720


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## SPEEDO (Jun 9, 2003)

on those, they have a FICD solenoid(screws into the lwr half of carb) the needle maybe stuck..


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## VaGeo (Oct 23, 2021)

SPEEDO said:


> on those, they have a FICD solenoid(screws into the lwr half of carb) the needle maybe stuck..


I have an 83 z24s, new carb, crazy high idle, emissions unplugged .. new electric choke, can't get idle down. Found 1 screw that appeared to be idle, it's not touching


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## jp2code (Jun 2, 2011)

VaGeo said:


> I have an 83 z24s, new carb, crazy high idle, emissions unplugged .. new electric choke, can't get idle down. Found 1 screw that appeared to be idle, it's not touching


I don't know much about the 83 model.

I'd look for vacuum leaks and check the ignition timing with a timing light.


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