Irregular idle

I have a 94 Suburban with a 350 motor. Just in the past week, I've noticed that after starting it (just when it's cold), the idle lopes a bit. After it's warmed up, the problem goes away. What should I be
looking at to diagnose the problem?
Thanks
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Have you scanned the computer for any error codes?
http://www.georgiasyty.com/aldl.htm
Doc
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FWIIW, My 96 Sonoma's idle was irregular the time I left the oil fill cap off (it even stalled a couple of times going to work and back that once ~20mi). It seemed to stabilize after a while running too (before I found the oil cap was off). Thankfully the cap stayed near where I had set it down. I put it back on and the idle was normal again. I figured it affected the vacuum indirectly through the PCV, and that other vac problems could easily have a similar effect. It didn't set any codes either. Elliott
\"Doc\" wrote:

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No, it didn't effect the vacuum indirectly... Leaving the oil cap off allowed air to enter the engine that wasn't measured by the Mass Airflow Sensor (MAF), thus, the fuel mixture and timing were calculated wrong.

Because the PCM has no way of knowing whether the air is being measured correctly other than the MAF sensor, and if you allow air to bypass the MAF, it doesn't know it.
None of this is anything new.... Volkswagens did the same thing back in the early 70s. (my first encounter)
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Neil, Sounds like your description is more accurate to how the computer sees it. I was thinking simplistic (ie: the PVC sucks a vac onto the crankcase). It did seem odd that the PVC could allow that much vac-leak - I guess not. Elliott
Neil Nelson wrote:

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Neil, How does the air get from the crank-case into the intake manifold? It's not a 2 stroke:). Elliott
Elliott wrote:

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Air enters the breather tube which is plumbed after the MAF, it is drawn thru the crankcase where it picks up the blow by and oil vapors, then it goes thru the PCV valve and into the intake manifold. IOWs, a standard PCV system except that the breather tube (crank case inlet) is situated that air must go thru the MAF before it reaches the breather.
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Thanks Neil, Was also wondering if you think the PCV can draw enough air to corrupt the other vac lines? Elliott
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snipped-for-privacy@comcast.net (Elliott) wrote:

If he vacuum leak is big enough, it can effect other vacuum circuits.
Got called over to another shop Wednesday. 92 Lumina with a 3.1 V-6. Runs like crap. Low amps waveform of the ignition primary strongly suggests that there is at least one shorted coil primary, shop owner replaces coil pack, waveform now looks good but the engine still has a miss-fire. (runs better but not right yet) We check the injectors, good current flow there. Connect scope to secondary, firing voltages sky high in the 40KV range. Hmmm, has to be running lean and it's effecting all cylinders, connect scanner to check the fuel trim numbers, yup, it's off enough, MAP voltage is 3point something volts, I pull the breather tube off of the intake snorkel to see if maybe I can feel a stronger than normal vacuum that might suggest leaking intake gaskets. The vacuum on the -breather- tube damn near tears my thumb of it so strong. Yesterday the shop owner tore the top of the engine apart....
Cylinder #3, a very large portion of the roof of the intake port in the head along with the intake rocker and stud is just lying there! That's probably the worst vacuum leak I've ever seen!
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I've got a little more info on this problem. I've checked for vacuum leaks and checked the PCV valve. Everything looks fine there.
The vehicle is hard to start when it's cold; I crank the engine to the point where it feels like its ready to go, but then it just dies. After it's been started it idles high and irregularly - the tach shows it idling between 700 - 950 rpm. After its warmed up, just couple of minutes, the idle evens out and falls down to under 500.
Could it be a problem with the injectors?
Steve Lewis wrote:

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