okay guys i got a 1989 camaro iroc with 5.7 tpi and auto trans. this car has had no mods done to it it literally is the original motor etc..... now here is my problem. i can set the timing and yes i do it by un hooking spark advance wire at set it at 6 degrees just like my haynes manual says to. it will run great pulls really hard but only for a few miles then randomly the idle will go from 600 to like 1500 even sometimes 2000 rpm. i had the dealership change the tps and iac plus it has a tune up and brand new coolant temp sensor. so it does that randomly but it will also come out of it randomly then will run fine then back again.

i have no vaccum leaks or coolant leaks,oh the dealer here in town has good techs whom i know but seem stumped plus i have no codes.

 

If the base timing is truly changing, then the star wheel on the distributor shaft is loose. Will need a new shaft assembly.

As far as the idle speed increasing a vacuum leak will also cause that.

RBob.

 

So its idling high, your title is confusing. They should scan it for iac codes & smooth tps operation. Check the ecm grounds, sometimes all you need to do is loosen them & retighten them, they should be on the back of the heads. It might have a vacuum leak at one of the plenum gaskets, see if they have a smoke machine.