still looking for ideas

[duckle1]

so your saying that if I wait until the engine is cold(when it does the idle thing) unplug the coolant temp sensor then start it, If it idles right then I have a bad temp sensor? I just replaced it, plus my check engine light is always on and the truck will not comm...with a scanner.

[junior3382]

If it refuses to communicate with a scanner, perhaps the problem is actually in the computer. Have you tried either testing the ECU directly or replacing it?

[duckle1]

Originally Posted by 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.

What is TSB you mentioned on PM. If the pcm has lost memory and truck is still running,should I just live with it? all the wires seem OK,same with fuses,besides if the temperature outside is 50 or above the truck Idles fine.

[crabtruck]

TSB March 2003 #01-06-01-028A
Engine Knock on Cold Start
1999-2002 Chv/GMC C/K PU & utility,
4.8,5.3,6.0L VINs V,T,Z,U -RPOs LR4,LM7,L59,LQ4

Some of the above vehicles may exhibit an engine knock noise that begins in
the first 12-15,000mi. The knock noise is most often noticed during initial
start-up and typically disappears within the first 5-30 seconds (may last
longer in extreme cold temperatures). The noise is usually more noticeable
on the initial start-up when the temperature is below 10C(50F) and may be
more pronounced on the first cold start following a long trip.

The noise may be caused by an interaction between carbon that has
formed on the piston, the piston motion and the cylinder wall. GM (....)
has confirmed that the noise is not detrimental to the performance,
reliability or durability of the engine. THIS NOISE DOES NOT HAVE
ANY EFFECT ON THE LONGEVITY OF ANY OF THE ENGINE COMPONENTS.

[crabtruck]

Couple other stray ideas...in addition to looking for that short on the OBD data wire.
Actually measure the voltage for the TPS while it's doing the hunting thing.
It should be steady.
Check that the knock sensors haven't been fouled by your oil leak.
Check your O2's are good, meaning measure them not just buy new.
Too bad you can't borrow a cal-pak (prom) for a couple minutes.
By losing it's memory I meant "mind" not learned fuel trims.

[tonyvt]

Originally Posted by 436'd skylark

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

My vote too!

Must be vac leak....

[duckle1]

Originally Posted by 436'd skylark

how does the power steering work?

a little noisey

[dawright_1988]

This is gonna sound bad, but... you may need to take it to a professional. At least you don't have to pay for anything until they fix the problem.

[436'd skylark]

Originally Posted by duckle1

a little noisey

There is a sensor in the power steering system that will affect the idle. if the PS system is acting screwy, the idle will surge big time.

[leolkfrm]

Have you tried a different type or brand of scan tool? sometimes different software in the tool will connect.