Rough engine idle/ service light is on.

[tnvol91]

I recently had my head gasket replaced at the dealer for my 5.3L V-8 1500 4X4. My wife picked it up and drove it about 20 miles. She noticed the engine began to run very rough. Upon returning it to the dearlership it died as she rolled into the parking lot. They diagnosed a bad fuel control valve and replaced it Everything was fine until 24 hours later. Now, the engine runs extremely rough and the idle rolls up and down bewteen 400 and 900 rpm while at a stop light in drive. My wife didn't seem to notice this when she drove it before the fuel valve replacement. The service engine light came on not too long after the engine started running EXTREMElY rough on the interstate. If you let it coast from a stop in drive, the truck lurches forward badly. I have read almost everything related to this on the site but don't see anything good coming out of this. Thank goodness I bought an extended warranty.
Any ideas on what is going on with my beloved Silverado.?(I need to tell my wife something so any info would be helpful.)

[bigbadben]

Yeah, i have the same problem. As a matter of fact I was working on it just this morning. I was told that the intake manifold is leaking. I could even prove it by spraying a little starting fluid down by the gasket. I've fixed it three times now. The first time with a new gasket. The second time we noticed that the surface looked warped. So we machined it nice and flat. Still didn't work, so we used some hi-temp silicone. Just took it for a drive and thought it was good. But then I went to park it and, well, it's not fixed. I dont know what else could be leaking though. Now that I've written a novel, i'll let you think about that.

[GMMerlin]

Originally Posted by bigbadben

Yeah, i have the same problem. As a matter of fact I was working on it just this morning. I was told that the intake manifold is leaking. I could even prove it by spraying a little starting fluid down by the gasket. I've fixed it three times now. The first time with a new gasket. The second time we noticed that the surface looked warped. So we machined it nice and flat. Still didn't work, so we used some hi-temp silicone. Just took it for a drive and thought it was good. But then I went to park it and, well, it's not fixed. I dont know what else could be leaking though. Now that I've written a novel, i'll let you think about that.

How did you machine a plastic intake?
5.3 engines have a plastic intake that will crack underneath and cause a vacum leak

[tnvol91]

No problems now. I wheeled into the dealership and we found the problem right away. When they put the spark plug wires back on one of them was not properly seated on top of the plug.