I'm an old muscle head and know my way around maintenance and mechanics very well on the old carbureted stuff. Attach a wire, sensor or a computer to it and I get instantly stupid. Please help!


I have a "97" F-250 with a 460 TBFI and 88k miles. It's the newest truck (anything) I have ever owned. I have owned it for two years now and it has always idled too high. While troubleshooting a recent auto trans shifting problem I was led to the Throttle position sensor (Because everything is electrically connected to everything!). I tested the TPS with my meter as per my Hanes book and it didn't meet the voltage parameters specified so I installed a new TPS. YAY! The new TPS solved my transmission shifting problem and dropped my idle RPM from 1300 to 1100. Again YAY! However.


My question is: Can any of you "smarter than me" Ford folks help me get my idle speed down to 800-900 RPM???


The Idle set screw is backed completely off, it has a new TPS and is a bit worse in colder weather. Head gaskets were replaced 10 months ago and there is no difference before and after, so I highly doubt I have a head/intake vacuum leak and I have scouted all of the vacuum lines which "appears" ok.


Thanks kindly for any help!

 

First off it does not have a Idle set screw. That is the throttle stop screw and is set at the factory and not to be touched or you run into a sticking throttle problem.
It is also a 460 EFI and not a TBFI engine.

If you have no vacuum leaks the the Idle Air Control (IAC) valve may be stuck.
You can try cleaning it but if you do do not get any cleaner in the windings.

It is also normal to idle high for the first 2 or 3 minutes.

 

Thanks for the education Bill K.


I will figure out and pursue the IAC valve possibility.


What should I do now that I have screwed up (out) my throttle stop screw?

 

mine idles at 1000 rpm all the time

 

Hardlanding also has a point. Not the 1st 460 I've heard of idling at 1000rpm.

Another idea is, are you basing this off the factory tach or a timing light with tach? I know both my trucks tach is off by 100 or so rpm. And there was another user on FTE that complained of his 460 idling high and he did the exact thing in bottoming out the Throttle Stop screw. After sitting it where the blades didn't stick or bind in the bore, and used a timing light with tach, he found his factory tach was off 100+ rpm.

Hope this helps!

 

The IAC valve sets just in front of and below the TB (Throttle Body).

There is a long process but most just turn the screw to get about 0.90V on the TP wire at closed throttle.
There should have been a note attached to the TB about the screw.

 

I would guess either vacuum leak,idle air control valve or map sensor(manifold absolute pressure).passenger side right below hood on firewall