i have an 89' 4.3L, and i recently did a complete tune up to it, and it still is having idle problems. When it is in park it will idle really low when i first start it and it dies sometime if i don't give it a little gas, then if it gets to where it will idle w/out my help on the throttle, it will get to where it almost dies then on its own it idles really high around 2500 rpms for a little bit before going back down to way to low. and it just repeats this up and down cycle?
any advice would help.

 

Several things come to mind but here's a few:

Could be a vacuum leak, and the idle control motor/computer is trying to compensate.

Could be the idle control motor

Could be low fuel pressure - either regulator or fuel pump

Could be fuel filter

 

Might want to check function of the EGR valve too.

 

I think vacuum leak.

Surging engines can be EU searching for right idle absent of proper vacuum.

 

Alright ill try all those and see which one works. thanks

 

If you pull the EGR off, you can replace the gasket with a screened one that could prevent future jamming of the valve.