I've been trying to sort out why my vehicle idles too high. I found a bad vacuum line attached to a mysterious part. I have no idea what it is. I looked it up in my Haynes manual and I think it might me my Throttle Positioning Sensor, but I don't know. The picture wasn't very clear in the manual.

Here it is after I pulled it out:


Here it is installed (note the messed up vacuum line on the right):
http://i1089.photobucket.com/albums/...-56-00_284.jpg

And here it is on the overall engine:
http://i1089.photobucket.com/albums/...-55-39_366.jpg

 

Looks like a vacuum switch probably for emissions things, just replace the hose and reinstall, those things usually dont go bad.

 

I already did that. I'm still searching for the cause of my high idle speed, but at least that vacuum line is no longer a suspect.

 

Take some carb cleaner and spray around, see if the idle changes you found a leak.

 

See the 9C915 in the center of the engineering number, that is the basic part number, the prefix and the suffix will identify the actual application. Call Ford parts to identify for actual application. Agree with above member, looks like a vacuum switch, probably for the carbon canister.

 

Sorry, overlooked the reason for your question, the high idle. Don't overlook the large vacuum line to the booster, mine had a crack in it, although idle was perfect with hood open and in neutral, it surged way up in high torque conditions. Keep looking for air enterring the intake system.

BTW, is base idle set correctly?

 

@good old bill: I have no idea whether the base idle is set correctly. I'm working through the vacuum system before I start playing with idle speed.

 

That piece is part of the emission system. If you replaced the line going to it and still no change, inspect all vacuum lines. If all ok then spray around the base of the throttle body and intake. More then likely have intake gasket leak

 

Btw what year and all if your truck

 

I'll do that tomorrow. It's too dark to work on the truck tonight.