high idle problem
Thread Starter
|
Cargo Master
Joined: Oct 2007
Posts: 2,712
Likes: 107
From: BoCoMo
high idle problem
Hello friends, I have a 1991 F-150 inline 300 6cylinder. It is a five speed manuel tranny. I do not drive this truck very often as I let my 16 and 21 year old girls drive it. I have now noticed that for some reason it is not idleing down.... it will always remain over 1500 rpms. I can set it in neutral and at 'a' Park... Rev the engine up and it will come back to 'around' above 1500 rpms and after about 3 seconds will 'stall' and drop quickly to under 900 rpms (this is 'around' the idle speed) it will stay there for about 2 seconds and then slowly climb back up to over 1500 rps. and stay there, unless I 'rev' it up again and it will go through the same pattern.... come down to 1500 rpms... 'stall' after 3 seconds and then slowly climb back up. I can find no linkages that are binding. It drives fine and shifts into all gears fine.... coming to a stop sign it will 'idle' high...'stall' to 900 rpms and then climb back up... I have a full shop manuel to go over anything, but I am at a loss on where to start looking for a solution. any suggestions will be welcomed.
Thank-you
Brother Les
Thank-you
Brother Les
Elder User
Joined: Nov 2005
Posts: 834
Likes: 0
You might have a vacum leak, but the 300 is not known for developing them at the intake.
I would first look at the Idle Air Control, IAC. The IAC can be removed and cleaned. Sometimes this will solve the problem, but if it is really bad, it may need to be replaced. Your shop manual probably covers the proceedure.
If you do check for a vacum leak, try using a propane torch , unlite of course. Moving the torch tip around suspected area allows the propane to be pulled into a vacum leak and increases the idle speed. Can't get the torch tip in some places, but works nice where it fits. Using propane eliminates the potential for a fire from the carb cleaner and potential solvent damage to wiring and vacum lines.
Good Luck Frank
I would first look at the Idle Air Control, IAC. The IAC can be removed and cleaned. Sometimes this will solve the problem, but if it is really bad, it may need to be replaced. Your shop manual probably covers the proceedure.
If you do check for a vacum leak, try using a propane torch , unlite of course. Moving the torch tip around suspected area allows the propane to be pulled into a vacum leak and increases the idle speed. Can't get the torch tip in some places, but works nice where it fits. Using propane eliminates the potential for a fire from the carb cleaner and potential solvent damage to wiring and vacum lines.
Good Luck Frank
