Fast Idle issues

Tiny
BKERN92
  • MEMBER
  • 1986 FORD F-150
  • 4.9L
  • 6 CYL
  • 4WD
  • MANUAL
  • 150,000 MILES
When I start my truck it idles slightly high around 2000-2300 rpm in neutral or clutch pushed in. Once I start to move the truck seems like the rpm go down to around 1500-1700 rpm. The rpm are mostly higher when clutch is pushed in or in true neutral. Do you have any idea what it may be? Or at least some things that I can check to get me going in the right path?
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Saturday, December 26th, 2020 AT 1:14 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • EXPERT
Have you checked for vacuum leaks? Have you checked the idle air control valve (IAC)? The IAC, located on the throttle body, is responsible for maintaining the engine idle speed.
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Saturday, December 26th, 2020 AT 1:14 PM (Merged)
Tiny
RAMIRO GARZA
  • MEMBER
  • 1982 FORD F-150
  • 5.0L
  • V8
  • 2WD
  • AUTOMATIC
  • 300,000 MILES
My truck idle will go high then shuts off.
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Saturday, December 26th, 2020 AT 1:14 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

What you described could be a few things. If the vehicle is being starved for fuel, it will lean the mixture and increase the RPM's then stall. If you haven't already, check to see if that is within spec. Here are the directions:

1982 Ford Truck F 150 2WD Pickup V8-302 5.0L
Fuel Pressure Test
Vehicle Power-train Management Fuel Delivery and Air Induction Fuel Pump Fuel Pressure Testing and Inspection Component Tests and General Diagnostics Fuel Pressure Test
FUEL PRESSURE TEST
PRESSURE TEST
1. Connect a suitable pressure gauge (0-15 PSI) to the carburetor end of the fuel line.

WARNING: Use care to prevent combustion of spilled fuel.

2. Start the engine (it should be able to run for over 30 seconds on the fuel in the carburetor bowl) and read the pressure after 10 seconds. If pump pressure is too low or too high install a new fuel pump.

Fuel Pump Pressure .................... 6.0-8.0 PSI

3. Reconnect fuel line at filter and install air cleaner.

______________________________________

If that isn't an issue, then check to see if you have any engine vacuum leaks. Here is a link showing how that is done:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Let me know what you find.

Take care,
Joe
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Saturday, December 26th, 2020 AT 1:14 PM (Merged)
Tiny
GARY L CAINES
  • MEMBER
  • 1915 FORD F-150
I have a 1993 F-150 4X4 5-speed manual transmission 302 engine with 170K miles on it. Often when driving, the idle speed will increase to as much as 3000 RPM between shifts. Sometimes I can go a couple of weeks with no problem. Sometimes it has the problem almost continuously. Temperature does not seem to affect the problem. The truck and drive train are in excellent condition and nothing has ever been worked on since new.
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Saturday, December 26th, 2020 AT 1:14 PM (Merged)
Tiny
GABE
  • MEMBER
Try changing the throttle position snesor
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Saturday, December 26th, 2020 AT 1:14 PM (Merged)
Tiny
HEAVYDUTY
  • MEMBER
Have the idle air control (IAC) checked
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Saturday, December 26th, 2020 AT 1:14 PM (Merged)
Tiny
CHRISM
  • MEMBER
  • FORD F-150
On my f-150 pickup she will rev. Up to 2000 rpms when I push the clutch in. Why?
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Saturday, December 26th, 2020 AT 1:14 PM (Merged)
Tiny
DAGGS
  • MEMBER
Find out if your f 150 has an idle air control valve fords usually have those on there fuel injection systems and that could cause it I has the same prob on my mustang
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Saturday, December 26th, 2020 AT 1:14 PM (Merged)
Tiny
CHRISM
  • MEMBER
It does have an iac valve
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Saturday, December 26th, 2020 AT 1:14 PM (Merged)
Tiny
2CEXPT
  • MEMBER
Throttle body may have coked up-clean it out especially around the plate then comeback.
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Saturday, December 26th, 2020 AT 1:14 PM (Merged)

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