Hi all, I am new here as I just started working on a new to me f-150. Seems like a solid truck except the idle is way to high. I have done a pretty thorough research and have tried a few things with 0 effect. When I first got the truck it was idling very low, and stalling when cold. I did the valve seals and a tuneup. When I restarted the problem appeared. I tried TPS, IAC, Cleaned the butterflies, checked for vacuum leaks. The is just a hair crack of daylight on the TB which I assume is normal. I guess my next move is a map sensor and then the stealership. I didn't mess with the EGR because the plastic vacuum lines are breaking right and left. Thanks for your help in advance...Joel

 

Welcome to FTE. If the issue started after you most disturbed those brittle vacuum hoses you most likely broke or cracked some.

First thing to do is run the Key One Engine Off (KOEO) tests and stored code (CM) display. If the KOEO tests pass you will get System Clear Code 111, 111 (the codes are displayed twice). If there were failures then you will see the corresponding 3 digit code. Once that is completed any codes stored in CM will be displayed. If there are no stored codes you will see 111,111.

Once you know what the starting point is you can repair any issues flagged.

Another quick test, after you do the KOEO/CM display, is to start the engine then remove the connector to the IAC. The idle RPM should drop way down or the engine may stall. This means the root cause is electronic so that's why it's important to know of any codes before hand.

If the idle RPM remains high then you have a vacuum leak issue.

 

I Second the response stating that there may be a vacuum leak. On my 460 a rat chewed some lines and the idle increased greatly. You may be able to find the leaks just by listening for a hissing sound coming from somewhere on the engine.

 

Thanks, I will check more thoroughly.

 

I had some similar symptoms and I had a vacuum leak at the fuel injector o-rings. I also had a partial miss at idle and it turned out that the injector o-rings going into the manifold were rock hard and no longer sealing.

 

Hello again, I searched for leaks and found 2. I plugged both those leaks and it made no difference. I did notice that a red line that I had broken when doing the seals was drawing air. I thought I had replaced both ends of this line. My problem is almost certainly a misrouted line or something. Can anyone direct me to a diagram a novice can understand? Thanks

 

Please disreagrd. I found some decent diagrams with a little research. This website is great. Here's my contribution, Chevy's are worse!