still looking for ideas

[duckle1]

1999 silverado, 1500, 2wd, 4.8 vortec ,FI ,364,299 miles. changed fuel filter, plugs, wires, tps,MAP checked ok,IAc LOOKS OK, changed all fluids, It leaks a little oil, I even pulled the EGR and cleaned it and put a new gasket on,, I added gumout, Put lucas with the oil, checked MAF sensor, air filter is ok, I changed the coolant temp sensor also....But no matter what I do Every morning Or when the truck has had a lot of time to get totaly cold,I start it and it Idles up and down 300 to 1500 until it gets warmed up then it sits right at 600 like it should I,m at my wits end ,any Ideas?P.s. Truck will not communicate with a scanner, My coworker has a 2001 chevy sierra(pretty much the same truck, It started Idling crazy inthe mornings this winter but has mysteriously stopped, He had put it on a scanner and it never threw a code..)

[crabtruck]

Maybe I missed it in the list of things, but have you checked the PCV ?
You could say the idle speed is a result of air flow from the following sources:
IAC, PCV and any vacuum leaks.
The eratic idle you describe (hunting) can also be caused by variances in the supply voltage to the IAC.
That can be from something as simple as poor connections from battery
to the grounds and hot spots. Make sure they are clean and tight.
An EGR that is on at idle can cause roughness too I believe,
but doesn't sound like what you have.
I'm kinda betting on the vacuum leak, especially since it disappears as the eng heats.

[436'd skylark]

I would check for a vacuum leak. is the SES light on?

[leolkfrm]

You might want to put it on a scan tool and see what kind of info the coolant temp switch is sending the ecm it might be starting to fail

[436'd skylark]

how does the power steering work?

[crabtruck]

Well, Joe, there is thing thing they call a steering pump under the hood....
Sorry, temptation strikes again. I think he's chasing an oil leak right now.
Hmmm. Coincidence ? You decide.

[436'd skylark]

Everyone is a wise guy..

The reason I ask is there is a sensor in the PS system that detects boost and compensates the idle accordingly. I had to chase that down once before.

[crabtruck]

When I can't be actually wise...

[duckle1]

thanks for the advice,I,ve given up on the idle thing for now...at least until I find another good idea. how ever if its relevant to anyone when the truck is doing its cold idle thing there seems to be a ping right before it increases its idle ,but only till it warms up.

[jswindell]

Seems to me like a coolant temp sensor, it may not turn on the check engine light, but may be in the upper limits of it's operation. Try unplugging the temp sensor before starting up the engine. The ecm should default to the last drivable condition stored.