'92 F-150 5.8 High Idle?
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3rd Gear
Joined: Apr 2023
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'92 F-150 5.8 High Idle?
Hey All, I just bought a 1992. Stock it was a 5.0L AOD, but as some point it was swapped to a 5.8 (havn't checked the casting date yet) and left with the Light Duty transmission..
Currently the Idle if 1200 RPMs in park and 800 in neutral. Is that too high?
I'm new to trucks, but I know that would be normal for a 5.0 in a 3rd gen Firebird engine... but I'd assumed the longer stroke of a 351 would be closer to 800 park 5-6 Neutral. If it is to high would that indicate they left in the 5.0 ECM?
Currently the Idle if 1200 RPMs in park and 800 in neutral. Is that too high?
I'm new to trucks, but I know that would be normal for a 5.0 in a 3rd gen Firebird engine... but I'd assumed the longer stroke of a 351 would be closer to 800 park 5-6 Neutral. If it is to high would that indicate they left in the 5.0 ECM?
Lead Driver
Joined: Oct 2016
Posts: 6,185
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From: Houston/Sugar Land
Your idle should be around 750 RPM- 850 RPM. Pulling the connection at the IAC while idling should make the RPM's drop significantly and even possibly die. This is what you want to happen. It means your IAC is OK. If nothing happens when you disconnect the connection then the IAC is not working correctly. You can take it off and clean the plunger and the surrounding area with Throttle body cleaner. Good videos on what and what not to do when cleaning. You mainly do not want to get the cleaner in the motor part of the IAC. After it dries try it again and make sure the gasket is in decent shape. It if still doesn't do anything when you unplug it replace it and if still nothing when pulling the connection, try running diagnostic codes for some internal help.
Logistics Pro
Joined: Nov 2013
Posts: 3,921
Likes: 1,191
From: Mojave, Ca
Your park and neutral idle RPM should be the same. Your RPM should drop 100-200 RPM as you put it in any gear, IE Reverse, Drive, 2, or 1. As Sandy said, ~800 in park or neutral and ~650 in gear is appropriate. You may have a Throttle position sensor problem, but check the easy things first like the IAC, timing, and vacuum leaks.
Lead Driver
Joined: Feb 2002
Posts: 7,952
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From: Greater Austin, Texas
If nothing happens when you disconnect the connection then the IAC is not working correctly.
Yes, but not that the IAC is bad. It probably means somebody has jacked up the base idle screw. If this happens, first step is to back off the base idle screw to about 500 RPM, if it will go that low. If it will not, you may have other problems.
If a PO has jacked up the base idle, then the IAC cannot control the idle speed any longer.
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Anthony Hyde
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