bought my 89 w250 360 when I rev the motor the idle stays high and slowy gos down any one else have this problem is it the idle switch? there not cheap and I want to make sure if its that I don't think u can return electrical parts right?

 

I'm not certain how slow your talking but the computer will not allow the throttle to "snap" closed like a carb. The idle speed control motor will always catch the throttle returning and slowly close it.

 

It sounds like its operatjng normal...

 

no u rev it and it stays reving and slowly idles down on my 98 that has a tb too and don't do it

 

Your TBI system on your 89 is far different than what your other truck (apples to oranges).

It is possible your ISC motor is getting slow and worn out but it is hard to say over the Internet!

 

ok ill put up a vid next chance I get thanks

 

My ISC is making a lot of noise (kind of a sqeeling) and my 3.9L is doing much as you describe with the high idle. The ISC for the 3.9 is only about $50 but I have no idea what it would be for the 360.