starts, runs, but refuses to idle....
#1
starts, runs, but refuses to idle....
I have recently acquired a 1997 F250 LD (same body as the 150)the exhaust system is screwed(currently rebuilding it due to some IDIOT trying to cut out the cats with a grinder and cutoff wheel) and it won't idle (runs alright with a little finessing of the throttle) but after I get the exhaust rebuilt to where the O2 sensors get the proper flow I was going to clean the IAC valve but was wondering if the exhaust not feeding right would cause idle issues a well.
put things in a nutshell...the truck will run but will not idle. IAC Probs, Exhaust Probs, or combination of both??
put things in a nutshell...the truck will run but will not idle. IAC Probs, Exhaust Probs, or combination of both??
#3
Conjecture no.... Experience Yes.... I am not overly familiar with these newer electronically controlled engines.
I actually specialize in the old Iron block Pontiac V8's and I have been tinkering with my 1988 IDI Navistar since about 2006 but an electronic Ford 5.4 triton is a WHOLE Different critter than what I am used to.
I actually specialize in the old Iron block Pontiac V8's and I have been tinkering with my 1988 IDI Navistar since about 2006 but an electronic Ford 5.4 triton is a WHOLE Different critter than what I am used to.
#5
UPDATE!!!!!
I have finished rebuilding the exhaust(including Headers) back to intermediate pipes and have replaced the IAC valve and Fuel filter(old 1 was RUSTY as all hell)
I STILL Cannot get this damn thing to idle
Bought a Snap-on MT2500 and went through a whole series of checks including system data
Ruled out the TPS: closed throttle .95 volts with smooth travel thru to wide open at 4.77 volts.
IAC Valve is NEW as of about 5 hours ago.
Side note.... I also ended up replacing both the positive and negative battery cables(ends broke off of old ones) with OE Ford cables from Rock Auto and a New oil dipstick tube due to the old 1 being split.
Getting rapidly pissed at this truck..........
I have finished rebuilding the exhaust(including Headers) back to intermediate pipes and have replaced the IAC valve and Fuel filter(old 1 was RUSTY as all hell)
I STILL Cannot get this damn thing to idle
Bought a Snap-on MT2500 and went through a whole series of checks including system data
Ruled out the TPS: closed throttle .95 volts with smooth travel thru to wide open at 4.77 volts.
IAC Valve is NEW as of about 5 hours ago.
Side note.... I also ended up replacing both the positive and negative battery cables(ends broke off of old ones) with OE Ford cables from Rock Auto and a New oil dipstick tube due to the old 1 being split.
Getting rapidly pissed at this truck..........
#6
Well you still did not say what you see for live data.
Here is the info on idle.
The idle speed is set in program as about 650 +/- hot idle.
What is yours?
The Crank sensor measures the crank RPM as a signal back to the PCM so it can compare to the idle table in program.
If the crank signal is more than +/- 50 rpm the PCM adjust the IAC for air bypass until the correct idle is attained as measured by the crank sensor.
There after this loop/feedback action continues.
If the IAC is not able to physically adjust according to the PCM electrical control, the idle will not be to spec and under control..
.
If coolant temperature is not within spec for about 175 or higher the idle may be high because the system raises the idle by opening the IAC more assuming the motor is too cold and adds fuel to make the motor richer..
This could be caused by a stuck open thermostat or a faulty cylinder head temperature sensor.
The other possibility is an idle too low because the IAC is closed and not able to be controlled by the PCM.
.
Another issue that can affect the idle is an air leak but you would have a CEL and a code 171/174 present to tell you this.
Good luck.
Here is the info on idle.
The idle speed is set in program as about 650 +/- hot idle.
What is yours?
The Crank sensor measures the crank RPM as a signal back to the PCM so it can compare to the idle table in program.
If the crank signal is more than +/- 50 rpm the PCM adjust the IAC for air bypass until the correct idle is attained as measured by the crank sensor.
There after this loop/feedback action continues.
If the IAC is not able to physically adjust according to the PCM electrical control, the idle will not be to spec and under control..
.
If coolant temperature is not within spec for about 175 or higher the idle may be high because the system raises the idle by opening the IAC more assuming the motor is too cold and adds fuel to make the motor richer..
This could be caused by a stuck open thermostat or a faulty cylinder head temperature sensor.
The other possibility is an idle too low because the IAC is closed and not able to be controlled by the PCM.
.
Another issue that can affect the idle is an air leak but you would have a CEL and a code 171/174 present to tell you this.
Good luck.
#7
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#8
#9
Vacuum line or intake gasket leak. My intake gaskets had over 1/8" of carbon buildup. Causing a lean condition on both banks. It started showing symptoms in wintertime, loping idle, dying at red lights, but fine at driving speed. Then cleared up when it was warm. Last summer it didn't go away. Start with tracing all the vacuum lines one by one. Then look at the intake gasket seam. I could see a smudge of oil around most of mine. Then confirmed it by spraying a little brake clean on it, and the engine cutout. When I pulled the intake I knew I found the problem. It idles smooth as silk now. Oh, Don't forget the o ring on the heater line under there like I did.
#10
Idle at that rpm clearly shows that the IAC is not operating. It's closed.
It is not an air leak or hose causing that low an idle. It is 'lack' of air.
Do not adjust the throttle stop to control idle speed. Don't do it.
.
The throttle stop is specifically set to do two things. One, to not allow the plate to fully close as the 'base air' into the motor. Two, so the plate does not stick in the throttle bore when the throttle body cools down.
The base idle stop setting on a fault free engine allows idle at about 500 to 550 rpm with the IAC connector disconnected.
.
What to look at:
1. Has the base idle stop been changed?
If yes, move it up to the 500 rpm range. if not leave it alone for now.
2. If the removal of the IAC connector on a running engine does not change the idle find out why because it's this operation that sets and controls the Idle at the 650 +/- range where it is supposed to be.
.
Note the specified difference between the base idle and the operating dynamic ide.
This is so the system has a dynamic range to work over without being forced by a throttle stop limit.
Hence do not change the throttle stop on a normal basis unless it has been 'messed' with..
A mis-adjusted throttle stop can under certain conditions interfere with cold starting and high idle when it's not wanted.
If this idle system has been repaired after long term faulty operation, a PCM reboot is the best way to regain it's normal control providing no fault exist..
Good luck.
It is not an air leak or hose causing that low an idle. It is 'lack' of air.
Do not adjust the throttle stop to control idle speed. Don't do it.
.
The throttle stop is specifically set to do two things. One, to not allow the plate to fully close as the 'base air' into the motor. Two, so the plate does not stick in the throttle bore when the throttle body cools down.
The base idle stop setting on a fault free engine allows idle at about 500 to 550 rpm with the IAC connector disconnected.
.
What to look at:
1. Has the base idle stop been changed?
If yes, move it up to the 500 rpm range. if not leave it alone for now.
2. If the removal of the IAC connector on a running engine does not change the idle find out why because it's this operation that sets and controls the Idle at the 650 +/- range where it is supposed to be.
.
Note the specified difference between the base idle and the operating dynamic ide.
This is so the system has a dynamic range to work over without being forced by a throttle stop limit.
Hence do not change the throttle stop on a normal basis unless it has been 'messed' with..
A mis-adjusted throttle stop can under certain conditions interfere with cold starting and high idle when it's not wanted.
If this idle system has been repaired after long term faulty operation, a PCM reboot is the best way to regain it's normal control providing no fault exist..
Good luck.
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