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92 f-150 4.9 high idle

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Old 11-16-2010, 03:25 PM   #1
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Question 92 f-150 4.9 high idle

I recently got a 1992 F-150 with the straight 6. It seems to run great despite the 236000 miles, however the idle is very high. The engine never drops under 2200 rpm. Obviously this is not helping my mileage. With the truck warmed up I unhooked the IAC and the rpm drops to 1800, it doesn't stall just sits at 1800 consistently. Any ideas? While it is sitting at 2200 it idles smooth just wanna get the idle down to where it should be.
Thanks guys!
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Old 11-16-2010, 03:41 PM   #2
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Originally Posted by Joesparks View Post
I recently got a 1992 F-150 with the straight 6. It seems to run great despite the 236000 miles, however the idle is very high. The engine never drops under 2200 rpm. Obviously this is not helping my mileage. With the truck warmed up I unhooked the IAC and the rpm drops to 1800, it doesn't stall just sits at 1800 consistently. Any ideas? While it is sitting at 2200 it idles smooth just wanna get the idle down to where it should be.
Thanks guys!
run error code scans.http://www.f150forum.com/f10/how-ret...es-obdi-10907/

Check for vacuum leaks, & look to see if your throttle set screw has been tampered with.
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Old 11-18-2010, 08:58 PM   #3
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Default engine code 327

OK, I am getting engine code 327 - EGR valve position sensor, pressure feedback EGR sensor or EGR Pressure Transducer signal voltage to low.
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Old 11-18-2010, 09:04 PM   #4
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I'd bet on a crack or leak in the vacuum line between the EGR solenoid and the EGR valve.
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Old 11-18-2010, 09:16 PM   #5
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I'd bet on a crack or leak in the vacuum line between the EGR solenoid and the EGR valve.
You mean he might have blown off checking for Vac leaks when suggested? (that would be a first)
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Old 11-18-2010, 09:19 PM   #6
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The other idea (throttle stop tampered with)... you can pull the air intake hoses off of the throttle body and look at the butterflies while the engine idles. They should be almost closed.

If they are sitting open, back the stop screw off until they almost close - the idle should come down as you turn the screw.
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Old 11-18-2010, 09:22 PM   #7
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If it ends up being the vacuum leak, look up at the hood - there is a diagram on a sticker inside the hood. On my 91 5.0, it's a hot mess with those vac lines... It really makes sense after you study it, and we can help you sort through it too.
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Old 11-18-2010, 10:00 PM   #8
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Thanks guys, I will check try to check those in the morning and go from there.
I appreciate the help and your wisdom
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Old 11-22-2010, 08:02 PM   #9
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After checking and replacing most of the older vacuum lines, my father and I have come to the conclusion that the Tach is malfunctioning. We then hooked up a external tachometer and found the engine to be idling at a comfy 700 rpm.
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