Rough Idle Once Warm?

[alamantia]

Last year I bought a 1992 K1500 Blazer and drove it all winter and gave it a tune up in the spring when the ignition module went. When i first bought it I noticed it idled a little rough but figured it was just old at 160,000k and the rings were worn. When the ignition modlule went I replaced the module, cap, rotor, wires and plugs along with Air cleaner and PCV valve, belts hoses and thermostat & radiator. Still idles rough. Fuel pump went last summer, replaced that along with the filter. Put a new altenator and battery in it a few weeks ago. All said and done, still idles rough. Whatever, its old and the rings are prolly shot right? I notice that when i start it in the morning now that its cold out, it fires right up like a champ and goes straight to high idle, once it comes down off of high idle to normal idle the temp gauge is showing 120-140 degrees, it idles supurb, i mean like new, i cant believe how well it idles, not a shake stumble, nothing, now I know it is capeable of ideling like it should, once it goes up to 180 (180 stat) it idles like **** again, WTF? Should I take the IAC and EGR valves out and clean them with Carb cleaner? I could see if the heat is causeing the engine to expand and causing a vaccum leak between the intake runner and the head but I figured if it heats up any leak would close, not open? any ideas? Why does it idle fine when cold and like crap when hot? What causes that? Timing?

[johnjzjz]

i had the same problem 90 305 2500 truck , in the DFI it has a compartment i think its like a filter i dont remember its been a while but it was clogged under the injectors - it idled bumpy and was loosing power -- jz

[JSPERFORMANCE]

sounds like it only runs rough when it is trying to go into closed loop, could be an o2 sensor..

[alamantia]

Forgot to mention I changed the 02 with the tune up, I wish it was a clogged injector but it seems to pulsate correctly and it has no power loss, i sprayed the intake runners with carb cleaner and it didnt smooth out, i sprayed it down the TBI and it bogged which was good, im just confused

[JSPERFORMANCE]

have you scaned it? where are the block learns? where is the iac position?

[BonzoHansen]

Also check simple things...I had a bad spark plug to that to me - hairline crack.

[alamantia]

Thanks for all your help fellas, it was a crack in the friggin brake boster hose, go figure, I discovered it when squirting the manafold with carb cleaner last night. Thanks for all your help.