Question

A 2000 Chevy 1/2 ton 4X4, 5.3 V8. When starting the first time for the day, it will start right up and idle fine. But when you put it into gear, it sputters around for the first half minute or so. Then it's fine the rest of the day.

That's classic symptom of bad spark plugs or plug wires, but I've replaced both and it still does it. Scanned it and no codes set.

Does anyone have any words of wisdom? Bad coil, maybe? It has one coil for each cylinder.

If it had a distributor cap I would say it's cracked, but apparently it doesn't!

30 seconds....Heck, I wish I could get goin' that quick...I don't think I'd worry 'bout it too much.

Maybe the ECM coolant temp sensor is reading a warmer than actual engine temp,there by not adjusting the mixture properly.Mark

Dirty Mass Air Flow sensor.

oxygen sensor

If you don't have a scanner to read data or even codes, I would start with a cheap/free guess by cleaning the throttle body and idle air control valve. The IAC is on the top LH side of the throttle body, its pointed toward the alternator, and mounted by two screws.

It could also be the intake/plenum gaskets. I've seen a lot of these leak vacuum on cold starts and then not leak once engine warms up slightly, it can happen fairly quick in a minute or less. The old gaskets shrink and become brittle, when cold they leak vacuum but then swell slightly as temps come up. These would progressively get worse, to the point it won't idle good at all and have a check engine light.

Give it a good "strong" dose of Seafoam! May take 2 bottles and a total of $16 dollars. You just might be surprised.

Is the truck suffering from the infamous shutter and stalling?

99-2002 model 5.3 trucks engines had issues with low RPM's (below 700) when started first start of the day or pulling up to stop sign/lights, the RPM would fall well below 700 RPM and the engine would shutter, sometimes stall. The defect wouldn't trip a CEL or set a code in the computer. Two things to check, remove the plastic plenum cover, looking at the engine, on the drivers side, mid-center of the intake is a fuel pressure regulator with a rubber vacuum hose connected to it. Remove the vacuum line and tap on your hand or surface to check for residual fuel coming from the vacuum line. If you have fuel present, the diaphragm in the regulator is bad which will cause low RPM or shuttering. Second way to check, connect a fuel pressure gauge to the shrader valve on the fuel line. Start the truck, make sure the pressure is above 45 PSI. Shut the truck off, if the fuel pressure gauge goes to zero, that indicates the regulator is bleeding off and not keeping a constant pressure across the injectors.
Second cause is the idle control valve. It attaches to the throttle body on the left hand side. Its attached with two screws. The plastic bushing inside sometimes wears out which doesn't allow for a proper signal to the computer for pedal travel. If this is your problem, while you have the boot off the throttle body, clean the black crud out of the throttle body using cleaner and a rag. Make sure the air sensing ports in the throttle body are clear and not plugged with crud.

Hope this helps.

4play, I agree, you said exactly what I was about to post.

First thing I'd try is hosing out the throttle body with carb. cleaner, hold throttle open and get behind the plate too, wipe it all out clean.

Thanks for the responses! I should have a chance to work on it tomorrow afternoon. I think I'll start by checking the fuel pressure regulator. I have a gauge I can put on it.

If you have cooler weather where your at intake gaskets are suspect. Its a common failure point. Mine would start up fine but not idle until engine warmed up. About $50 for a new set and 3 - 4 hours to replace them.