help 92 chevy 454 idle problem

Hello, I Have A 92 Chevy 454 It Has A Really Weird Idle. It Idles At About 1000rpm And It Fluxuates Up And Down 200 -300 Rpm.service engine light is not coming on.. I Have Checked Every Plug To Everything And They All Check Out Ok. I Have Checked All Temp Sensors And Senders. I Have Replaced Tbi Base Gasket,egr Gasket, Tps Sensor ,map Sensor ,coil Plugs,wire,cap,rotor,iac Valve Even Adjusted It ,fuel Filter When You First Start It The Idle Is About Where It Should Be And After About 30 Seconds It Starts Going Up And Then Fluxuates.if i shut it back off and wait about 10 seconds it is back to normal idle for 30 seconds The Only Thing I Havent Checked Is The Egr Solenoid. Could Anyone Please Help Me Out.... Im just about to give up Thank You!!!!!!

Have you checked for intake manifold leaks, or vacume leaks in general?

i have checked for vacuum leaks everywhere cant find anything leaking at all.just had a gm guy run the ecm check and he told me temp sensor is showing bad so ill put another sensor on and try it but i do not think that is it.thanks Randy

I have a 91 454 speed manual with the same problem I have replaced the iac valve and the map sensor but still has the eradic idle and dies can you please help me I think it could possibly be the computer