Problem With Idle On '90 351W
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New User
Joined: Dec 2007
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Problem With Idle On '90 351W
My brother recently joined the Air Force and I am taking care of his truck while he's gone. He has a 1990 F-250 4x4 with a 351W & a 5spd. The RPMs sometimes fluxuate between 400 & 600 and often dies when the clutch is depressed coming to a stop. This can sometimes be avoided by using the engine to slow down. When the RPMs fluxuate it is accompanied by a voltage drop from 14V to about 9V. I have replaced the voltage regulator and the throttle position senor, but to no avail. Can anyone tell me what I am missing? Thanks.
Senior User
Joined: Jul 2007
Posts: 174
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From: G-VEGAS TN
rough idle
Somewhere in your system there is a short on negative side of the battery there is a plug that should feed the injectors power that may be the short ya might try that and jut for the heck of it jut unhook your battery with the engine off and see if the battery terminal spark if they do then that means you have a short
hope this helps
ole smokey
hope this helps
ole smokey
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
A surging idle is most often because of a sticky idle bypass valve (IAC), it can be cleaned with carb cleaner. On a vehicle this old you should also look for vacuum leaks, the juice can on the passenger fender is a vacuum resovoir and these rust out.
New User
Joined: Feb 2006
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The IAC is located on the inlet to your throttle body or just before on the intake. I am not familiar with the throttle bypass valve? You should pick up a Chilton or Haynes book, shows locations and some troubleshooting.
