High Idle
 

Hello

I have a 1988 F150 4x4, 5.0L. It is idling very high and will maintain 32MPH with foot off the accelerator. I cleaned the the throttle plates. I noticed (finally) that I had no Check engine light when starting the truck. I found that there was no bulb in the check eng lamp holder (sold to me thaty way). I installed the bulb and I now get a flashing check engine light when accelerating (ocasionally). I wanted to read the codes myself using the check eng light or a meter. Where is the test connector and what pins do a short and are there any other troubleshooting advice for the high idle.

i have an 87 f150 with a 5.0, dthe diagnostic hook up is on top of the right fender, its an orange box and it will say diagnostic on it but first off i would check for a major vacumn leak, like a pcv line fell off or one near the brake booster. good luck, post back let us know what you find

I had a similar problem and it was the PVC hose!

My '91 had similiar symptoms. I found the plenum-to-intake gasket tatered. an $8 gasket set and 2 hours to replace the plenum gaskets fixed all. I reset the PCM to erase the attempts to correct A/F ratio as well.

Thanks for all the input. It was the upper intake gasket. It looked as if it was going bad for quite awhile.