I have just bought my first truck, a 1991 F150 5.0 liter, and it idles at 1300 rpm parked, and 800 rpm In gear. My Dad and I have replaced TPS and IAC valve. Both are motor craft. The idle holds consistent, it just is high. Please advise. Thank you.

 

With the engine idling high, fold the brake booster hose. If the idle drops at all, replace the booster. Inspect the throttle linkage & cable for binding; disconnect the cruise cable from the throttle cable to see if it makes a difference. Get a digital multimeter & test the TPS:

 

When we binded the hose it dropped the idle from 1400 to 1300. The cruise cable made no difference. When we use the multimeter on the TPS, where should we take the reading from? Thank you.

 

That's addressed in Steve's caption. Click it and read it.

 

We had three wires. Black, green, and orange. We put the black probe on the black wire, and the red probe on the green wire. We got a reading of .95 volts.

 

Just wanted to hijack this thread real quick and thank Steve for all the great captions he provides. I've learned alot, and continue to learn from them. (Now all I have to do is start printing them instead of searching old threads for the one's relevant to me!) Thanks again Steve. Peace, Dave.

 

thanks guys! very helpful info!

 

I had problem with mine - rpms climbed up to 4000 - did some checking and found plenum bolts loose, gasket half gone, throttle body gasket bad, and a few vacuum lines dried cracked. fixed all that and now it runs great.