bouncing RPM's???
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Junior User
Joined: Dec 2005
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From: So Cal
bouncing RPM's???
my truck started rough a little rough and actually stalled one time. So i took off the IAC, cleaned it well, and clean the throttle body as well. Hooked up everything, went to start it...it started fine but now when i rev it up it kinda bounces coming back down. not to metion it still has a slight vibration of the whole truck. Please help!!
jason
00 F150
jason
00 F150
Lead Driver
Joined: Sep 2006
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First thing to do is re-boot the PCM so the old data is removed.
Then let it relearn the new IAC operation by several cold starts with the headlites and A/C or heater on so the loading is sensed..
Then see what problems are left to address.
Then let it relearn the new IAC operation by several cold starts with the headlites and A/C or heater on so the loading is sensed..
Then see what problems are left to address.
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Joined: May 2005
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Also check your plugs -- I had the same problem using bosch platinums, I couldn't figure out why my idle was rough at a stop sign, engine seemed to stumble a lot. My obdII reader didn't show any codes. Finally I took it to a ford dealer, and they traced it to the number 2 plug. Said it was flakey, replaced it with a motocraft, and charged me 230 bucks for the fix. All I can say is !@#@!@#$ I coulda replaced a lot of stuff for 230! No problems with the idle and roughness.. its fine. The mechanics advise was get rid of the bosch plugs, he says he sees ignition problems all the time with them in F150s. claims they don't fit well in the hole, or in the boot. In fact I gonna post another about this issue... good luck.
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Junior User
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From: So Cal
thanks for the info...i dont know when the last time the plugs replaced...also when im at a light or in traffic it idles around 100 RPM (almost dying)...would the plugs fix that? or would it be something else?
Lead Driver
Joined: Sep 2006
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I doubt plugs will be a fix but may be a small help.
The idle won't be much lower than about 550 rpm due to the throttle stop setting unless it has been adjusted. Engine won't run at 100 rpm.
If it regains speed with the throttle, this tells you you are letting more air in and the engine will respond to that.
It means the IAC is going closed with throttle closed and not recovering the engine idle by opening the commanded amount by the PCM.
The idle won't be much lower than about 550 rpm due to the throttle stop setting unless it has been adjusted. Engine won't run at 100 rpm.
If it regains speed with the throttle, this tells you you are letting more air in and the engine will respond to that.
It means the IAC is going closed with throttle closed and not recovering the engine idle by opening the commanded amount by the PCM.
Last edited by Bluegrass 7; Jan 14, 2007 at 08:14 PM.
Lead Driver
Joined: Sep 2006
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The IAC receives 12 volts on the red lead and is signaled from the PCM pin 83 thru the connectors.
Is the ground signal from the PCM there to allow operation?
If not, is the harness pin open or corroded? Lead is white/LB color code (on an 02).
These are the only leads involved or the IAC needs to be replaced.
If no signal from the PCM pin 83 then suspect the PCM.
Trying to play doctor from a distance is tough.
Good luck..
Is the ground signal from the PCM there to allow operation?
If not, is the harness pin open or corroded? Lead is white/LB color code (on an 02).
These are the only leads involved or the IAC needs to be replaced.
If no signal from the PCM pin 83 then suspect the PCM.
Trying to play doctor from a distance is tough.
Good luck..
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sometime my truck will bounce the rpm's at idle. like ill start it up and it will idle fine, then all of a sudden the tach starts bouncing going between 500 and 900 rpm's...if it give it gas and let off it will stop....but does anyone know why it does this on occasion? could it be the IAC valve?