89 f250 with a 351w, I changed upper intake gaskets and valve cover gaskets. Removed all smog stuff, now truck runs great just take forever to idle down.

Any ideas?

 

Is the condition the same when it's either cold or hot?

Your FAST idle, will stay till the truck is around 175*F, when started cold. The initial HIGH idle our trucks have, is usually for 5~10 sec.

May need to be more specific as when it occurs.

 

It happens hot or cold. When shifting between gears it revs up a little then takes 5 seconds before it idles down. 5 speed trans btw. Anytime u push in on clutch like slowing down, it revs small amount then after 5 seconds it idles down

 

Sounds like a vacuum leak. Any original "brittle" nylon lines still attached in the engine bay?

When you say removed smog stuff, did you remember to cap/plug off vacuum lines needed for the TAD/TAB solenoids and EGR valve?

 

What solenoids are u talking about?

I believe I plugged all the old lines. I will check again in morning

 

Checked lines. Nothing stands out. Any more ideas?