Please help with 460 engine problem
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Freshman User
Joined: Feb 2004
Posts: 38
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From: Georgia
Please help with 460 engine problem
I have a 94 F250 with the 460 engine (7.5 litre). It is speeding up by about 200 rpm for some reason. It will be idling at normal speed, then jump up about 200 rpm for about 5 seconds, then come back down.
In drive with the brakes on, it will be idling around 600, suddenly jump to 800. In neutral, it will be idling around 750, suddenly jump to 950.
As near as I can tell, it runs smooth with no fluctuations on the road, even at 40 or so at around 1100 to 1200 rpm.
Any and all help would be appreciated. Thank you.
In drive with the brakes on, it will be idling around 600, suddenly jump to 800. In neutral, it will be idling around 750, suddenly jump to 950.
As near as I can tell, it runs smooth with no fluctuations on the road, even at 40 or so at around 1100 to 1200 rpm.
Any and all help would be appreciated. Thank you.
Post Fiend
Joined: Nov 2008
Posts: 23,849
Likes: 20
From: McKenzie River
Fluctuations in curb idle rpm on a computer controlled engine are fairly normal, having the AC or defrost on will also run the compressor and make the idle speed change.......150/200 rpm change is negligible.
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Freshman User
Joined: Feb 2004
Posts: 38
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From: Georgia
How do I check the IAC?
BTW, if you think 200 rpm change in this critter is negligible, you quickly find out different when you are trying to park this giant thing in a tight place and it all of a sudden speeds up and jumps forward. As for this being normal, it has never done this before, just started it a couple of weeks ago and it has around 360,000 on it.
BTW, if you think 200 rpm change in this critter is negligible, you quickly find out different when you are trying to park this giant thing in a tight place and it all of a sudden speeds up and jumps forward. As for this being normal, it has never done this before, just started it a couple of weeks ago and it has around 360,000 on it.
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New User
Joined: Mar 2010
Posts: 18
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From: Wyoming County, Wv
Allow the engine to idle (at normal temperature) without anyone touching the gas pedal. Go under the hood, and disconnect the electrical connector to the IAC. If the engine begins to stubble or stalls the IAC is functional and does not need to be repaired.
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Lead Driver
Joined: Aug 2006
Posts: 5,670
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From: Sand Lake, MI
It should cycle open and closed rapidly during normal operation, if its worn or just dirty it may be hanging open at times causing the increase in idle speed.
Now if its unplugged while the idle is uncontrolled and higher then normal and it doesn't stubble and has little to no reaction to doing so, that would prove something.
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