2000 rough idle when cold

[Bodysurfer]

Merlin,
You were right!
Our 2000 suburban, (5.3) idled rough when first started,(the colder ambient the rougher the idle, it would start up and run fairly smooth for a few seconds then drop off to 300-400 RPM and rough for 5 seconds or so then back up to 2000 and smoother & repeat this cycle diminishing in roughness until warm). We took it to a reputable service center who spent 15 days doing injector balance test, injector flush, factory computer updates, 3 tankfulls of high grade Chevron gasoline, each time returning us the vehicle, we’d start it the next morning, cold, same thing & return it. I got fed up there & on recommendation of friends took it to another reputable shop. It was a similar,10 day-saga. They replaced plugs, new crank position sensor, did injector balance test, stand on our heads & cross our eyes to no avail. Finally the second chief determined the only thing left was the computer so off it went to the local dealership. The mechanics there couldn’t come up with an answer so they brought the techs in Detroit in on the case. The recommendation was to replace the injectors even though three balance tests showed they were good. Skeptical we stipulated that if that wasn’t the fix we don’t pay. They reluctantly agreed and installed a new set of injectors. When I started it up in front of them it seemed smooth, (however,ambient was only 60’ and engine might not have cooled completely even though I put my hand on it). I had a rough time making out a check for $1,122.00 but figured “what the hey’ if it gets my queen her burb back…” . The next morning after not running for 18 hrs.&40’ ambient., the exact same symptoms. Back at the dealership they now showed a MAP code and looked into the possibility of an intake manifold leak,( I had told garage #2 and Chevrolet about your diagnosis in November of intake manifold leak; your exact words were-“With a rough idle and a SES light with lean codes and random misfires, I would start leaning towards a vacume leak around the intake.Changing fuel won't fix that problem.” But apparently neither agreed with your assessment). Our communications can be reviewed at:
http://www.automotiveforums.com/vbul...4&goto=newpost
tagged on to somebody else’s-“Suburban Stalls”.
They determined that the manifold,(plastic),( must be warped & said they’d order a new one. I said “fine, but I’m not paying for those fuel injectors”. The service manager said he never OK’d the “guaranteed fix” (but one of his subordinates did). To his credit he refunded us the difference-$330. After replacing the intake manifold 1-15-04, ten weeks after we took it to the first shop, our suburban finally runs like a champ! Last week we went out of town with it. It did fine in 32’ morning start-ups. At a service station, while idling waiting for friends to finish filling up so we could get back on the road, she was purring so smoothly and quiet I turned the ignition to “start it up again”. I got that “spanking” you get when you send the bendix into the 500 RPM flywheel. It was bitter sweet!
My faith in your wisdom is reinforced. This is a neat web site. Bodysurfer out.

[GMMerlin]

Thanks for the kind words!