Always runs cool and idles erratic?

[lancetheman]

1991 2.3L Ranger 2X4 w/Auto Trans.
The idle is not stable. Goes up and down, but doesn't stall! The truck also runs very cool, even in traffic.
Any ideas what the problem could be? I was told to check electronic thrermostate?
One other thing, at back of engine there's a vacuum hose about 1/2" OD running from top of engine and going down between back engine and fire wall.
this hose is very soft and colapses, so not much vacuum going through it. I don't even know where the other end of it is? Have not got under truck yet to check.
Any help would be great.

Aloha, from Lance "the man" in beautiful Hawaii

 

[Mark_88]

Check for a MAP sensor on the firewall...that is known to cause erratic idle...and if the vac line to it is collapsing it could be the cause of the issue...can't remember where it connects to, but probably on the intake somewhere...

If you don't have a MAP sensor then the Idle Control Module might be wonky...if you don't have an ICM then there is something else controlling the idle that is probably on the wonk...