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Old 02-09-2017, 02:48 PM
Iron Port Iron Port is offline
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Question Idle Question?

When I start my Bronco It idles at 1200 RPM, Then surges between 1100-1000RPM and will jolt hard into reverse or drive and will want to accelerate up to 14 MPH without hitting the gas pedal. Is my idle to high and what is my Bronco supposed to idle at?
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Old 02-09-2017, 06:35 PM
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A little more information would be helpful to better help with your issue.

What year Bronco and what engine?
Have you tried checking for engine codes?
Is this idle only happening when cold or at all times?



When cold, most EFI controlled vehicles will be in 'Open Loop' mode which throws in more fuel to help bring the engine to proper operating temperature. The idle is typically higher in open loop, but it sounds as if yours is too high.

What I would first do is check for engine codes. If your truck is 1995 or older, checking the codes is incredibly easy. You just need a paperclip and need to jump two pins on the diagnostic port. It may be in a different location depending on the year of your truck, but the process is the same.

Here is a link that a user on another forum made that explains the process pretty well:
1983 Ford Bronco Diagrams picture | SuperMotors.net




If codes pop up, it would be a good thing to check those out first as the codes may be relating to your problem.

Off the top of my head, things that CAN cause high/erratic/incorrect idles are:

-Vacuum leaks
-Dirty/bad Idle Air Control Valve
-Bad Throttle Position Sensor

Usually a messed up idle isn't that big of a fix, but finding the issue can sometimes be tedious. I'm sure you'll be able to correct it though with the help of people on this forum!
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Old 03-17-2017, 09:59 PM
Iron Port Iron Port is offline
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Thank you max! I pulled code and got 17 different codes, Ouch. But many were for the TPS but before I checked codes I let it sat for a week when I tried to start it, it would crank and sputter. I spray starting fluid in and it even made it harder to crank! Could it be a bad distributor or pip?
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Old 03-19-2017, 09:01 PM
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Please tell us about your Bronco.
year?
engine?
trans?
mods?
This will assist us in directing you to finding the cause.
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Old 03-23-2017, 09:25 PM
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I'm having the exact issue as OP on my 94 EB 5.8
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Old 03-30-2017, 10:33 AM
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To add an oddball cause of rpm idle surge to the list and yes when the surge happens you need to be aware or you may creep into the rear end of the car in front of you at the light.

My Bronco had a pulsing idle surge from 750 to 1000 rpm caused by the Air Conditioning in heater/window defrost mode calling for an increased idle rpm because Freon was low or the AC was otherwise defective.*

I know I need to rebuild the AC system sometime,** but in the interim I added Freon to the system with one of those little tanks with gauges and ... guess what?

My Bronco has had a steady idle at 750 rpm ever since.

So, the lesson here is that the PCM probably receives all manner of signals from all kinds of sensors attached to vehicle sub-systems some of which may tell the PCM to increase idle. And my odd ball experience here is that the correct signal coming from a defectively operating system can cause an inappropriate rise in idle.


* Does your AC clutch engage when your idle surges?

** Bubba, was it you that graciously sent me the info on how to rebuild the AC a couple of years back?
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