Hey guys,
My 92 F-350 460 (in sig) runs and drives great, but when I'm stopped in gear it idles low. When its first started it idles higher in gear like 700-750 but after a few minutes I come to a top and the idle in gear it seems to be about 550-600. When it idles that low it just feels like its missing or something.
Just did a tune up (plugs, cap, rotor, wires, coil, iac and throttle body cleaned, new injectors and fuel filter) its always done this since I have the truck just idles lower then my buddies 97 in gear.

 

After its warmed up and in gear

 

When it's first started and about where my buddies 97 is all the time. Sometimes it's a tad higher then that but not much.

 

Anyone ? ?

 

Looking at the odometer, 10000 miles later, its hard to say.

First thought is sticking IAC valve
Sexondt thought is someone tampered with the Idle Stop screw on the throttle body.

When the engine has fully warmed up, and the rpms are low as you noted, unplug the IAC connector. If the rpms drop further and/or the engine dies, I'm inclined to believe it's working. If the rpms don't drop, then remove and clean the IAC valve.

Look where the throttle stop screw is located. Does it appear to still be loctited in place or has it been adjusted?

 

It's always done this. Iac has been cleaned and has also been replaced.

 

The TPS is at .9 volts

 

Ok, you said its done this since you have owned it. Is that since it was new or you bought it used at some point?

Did you perform the IAC test? If the Idle doesn't drop or engine dies when you disconnect it, then its not being commanded to increase air flow.

Does the Idle stop screw look to be tampered with it or is it still loctited in place from the factory with yellow or orange paint?

TPS readout can vary between all vehicles and isn't necessarily an indicator of whether or not the Idle stop screw has been adjusted by someone.

 

Iac disconnected drops idle even lower. The stop screw looks to have been moved but it's in the same spot. Hard to tell the loctite is so old and barely visible. I bought truck used with 92,xxx and it's done it since. It doesn't stall but starts to get a slight miss/rough idle when it drops to the spot it is in the picture.