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Old 03-14-2019, 11:19 AM
Chalax Chalax is offline
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Default High Idle Ranger 1998

Hello,
this is my first post on this web page as I have decided to make an account and start being a part of this community which seems to be quite active.

I've looked the internet for weeks for a fix to my current issue and haven't been able to find a fix.
I know I am not the only one and we deserve to have ONE thread where this issue gets fixed.

Pretty much I am going to repeat what has been already written in other pages (but these don't seem to have a fix for everyone).

Whenever I turn on the engine, the RPMs go quite high for like a second (2,000+) and then come slowly back down to under 1k.
So far so good, the RPMs will stay like this until you hit on the gas pedal.

As soon as you do, RPMs go up (obviously) but will not come back down to under 1k and will instead stay between 1.2k-2k and sometimes even 3k.

While cruising, the RPMs stay up, I call this The Poor Man's Cruise Control. As one does not need to keep his foot on the pedal to keep the RPMs high.

When shifting (clutch on) the RPMs go even higher! Putting a high load on the engine and the new gear.

I've cleaned the throttle body, MAF sensor and connector, Cleaned TPS connections, Checked TPS with a voltimeter and it seems to be working as intended (no voltage spikes), cleaned the IAC and even changed it for a new one.

So far, Ive gotten this code which I think may be the only relevant one:
P1504.

Any idea of what else can I do to fix this issue? Hopefully we get to fix it for everyone else in the future having the same issue.
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  #2  
Old 03-14-2019, 11:31 AM
Mike4x4 Mike4x4 is offline
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Default Re: High Idle Ranger 1998

I'd start with checking for a vacuum leak. That might be the cause of your high idle. My intuition tells me that the IAC would be suspect but you said you cleaned it.

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Old 03-14-2019, 11:39 AM
zpn_by zpn_by is offline
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Default Re: High Idle Ranger 1998

+1 on vacuum leak check. Iíd still be suspicious of the IAC, as Iíve had them bad enough that a cleaning doesnít work. Also ensure that your throttle cable is free to move. After 20 years, itís possible that itís been kinked or somehow gummed up. Check all you vacuum lines though, as some of those hose ends get dry rot and crack.
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Old 03-14-2019, 11:43 AM
Dirtman Dirtman is offline
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Default Re: High Idle Ranger 1998

Definitely an IAC problem. The IAC is pulsed to ground by the ECM to determine how much it opens, if the IAC gets shorted to ground it will stick wide open. Your code p1504 pretty much confirms this is the case since it is a circuit malfunction code.

First, with the engine idling unplug the IAC valve connector. The engine should drop in RPMs to 500 or less and maybe even stall. This means your IAC is definitely sticking open. If the engine remains at high idle you have a vacuum leak.

The issue however is most likely a short in the wiring. You need to very carefully trace the wires and check for any breaks, cracks, or corrosion. Though you also want to check the solenoid itself is not internally shorted. Check for continuity between both terminals of the connector and the metal case of the valve. There should be none. The solenoid is not grounded to the block, its grounded by the ECM so continuity between either terminal means its shorted internally. And just because it's new doesn't mean its good. Check anyway.
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Old 03-14-2019, 11:45 AM
Chalax Chalax is offline
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Default Re: High Idle Ranger 1998

Indeed 20 years are quite a bit.

I did clean the OLD IAC and later replaced it for a NEW one. Right now it is using a the new one and the problem persists. I have looked for vacuum leaks but I cant seem to find any.

I've read other forums where people say that they couldnt find any vacuum leaks either.
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Old 03-14-2019, 11:47 AM
zpn_by zpn_by is offline
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Default Re: High Idle Ranger 1998

Dirtman, thanks! Iíve been away from older Fords for a few years, so I appreciate you adding that! Guess Iím rustier than my truck!
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2002 Explorer 4.6 Eddie Bauer 4x4
1999 Ranger Supercab 3.0 5-spd RWD
1986 Ranger 2.9 RWD
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Old 03-25-2019, 09:18 PM
Chalax Chalax is offline
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Default Re: High Idle Ranger 1998

I wanted to give an update on my truck situation.

I changed the plug cables and the idle went down to around 900 RPMs.
Anyone knows where should it be around?

Also, I am now getting a P0172 and P0175 codes.
I have also noticed that the o2 volts reads 0 and it stays there. I've read they should be going up and down between .1 and 1 volts?

I removed both upstream o2 sensors and tested resistance on both the white cables, which should be the heater cables. I am getting readings. Which means that they are working well... or should these readings be specific? I was getting something like .4 or something around that....
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