95 burb with a prob

hi all...hope someone can help.
1995 2wd Suburban 5.7 TBI with 295,000 miles.
No DTC codes present. All factory setup. Nothing added or Hi performance bolted on. Clean air filter ,fuel filter changed 3 months ago as well as PCV valve. Sprayed carb cleaner through the TBI and "de-gummed" it on a reg. basis.
No catalytic. Run low octane fuel.

Starts right up...idles perfect in park or drive around 1100 rpm.
Then after 10 min. of heating up it'll drop to its warm idle 600+.
Then the problem...it literally surges up and back down every few seconds like a wave...up to 1100 down to idle. Happens in Park or Drive, stationary or during travel, sluggish on accel at that time as well. After cooling period...starts all over.

Without a code....where should I begin?

Try spraying carb cleaner around the edges of the intake and around the base of the throttle body and pcv hoses. If you find a vacuum leak it will smooth right out. Use a bolt and plug vacuum line to the vacuum booster if it stops replace. Try plugging the vacuum to the egr and see if this helps if it does check the solenoid. Sometimes the vacuum control solenoid goes bad. With your mileage the egr is probably leaking unless its been changed.

Thanks for the fast reply...I will do all of that...when you say plug the vacuum booster...do you mean the line from the power brake booster?
Sorry to sound stupid...but this truck isnt hurting for "little plug-in" things...I want to make sure I try the right tests.

That's what I meant a leaking booster will cause idle problems. When you start the engine is running rich when it goes lean it misses a sign of a vacuum leak. These are just tests to locate the problem.

Cool....first thing...I'll do it.
I'm shopping for a EGR valve now just in case...there are over 5 types....mine hasnt a number on it...cause its older than dirt?

If you look at www.rockauto.com, there is only one ac delco egr valve for the automatic. See http://198.208.187.182/internet/PartImage.jsp?&acpartnbr=214-5074

//2000CAYukon

I think you should stay with a Delco many people get an aftermarket with the wrong flow rate and the vehicle doesn't run properly. The link is probably cheaper than the dealer.

Well...its fixed and running great!
Checked the booster for vac. leaks.
I sprayed the cleaner around the intake and TBI gaskets, no change.
I replaced the EGR, TPS, MAP and Vacuum Regulator Valve (shopping spree at Rock Auto).
Not sure which or combination of which was the fix. The new EGR wasnt "clocked" like the original, but I had some spare plastic hose and a right angle fitting from another project.
The parts were all original 1995 so I figured they could use it anyway.
The old EGR was rough looking.
The old Vacuum Reg. Valve didnt "rattle" like the new one...seems to have a check Ball/Valve like a PCV valve?
The old Vacuum Reg. Valve was also missing the sponge filter on one of its ports...wasnt aware 'till I saw the new one had it...maybe it had entrained dirt/contaminents?
Man, what a difference...idles great...takes off like its scalded and shifts through the gears including passing gear better than the day I got it!
I have to re-learn how to drive it!
I want to thank everybody involved in my project, saved me from dropping the tank and pulling a fuel pump...which at the moment , it doesnt need.