I have had a problem with my 1999 Cadillac Escalade 5.7L V8 Chevy 350. I bought it about a week ago. When the guy started it, it was running very rough. He told me that when he was driving back from the mountains that he heard a loud "POP" and pulled over and looked under the hood and found that a spark plug wire had popped off. He then hooked it back up and kept driving. When he started driving again it was running rough just like when I bought it. I drove it about 45 miles home and parked it in my garage. I have been a mechanic for about 17 years and had no idea what it was, but had a few ideas... I replaced the plugs, wires, cap, rotor, IAC, CTS, TPS, checked the spider injectors and thoroughly cleaned out the throttle body and MAF. Also replaced the MAP sensor. It seemed like it was running rich and idling very poorly. Almost as if it was mis firing. I would start it up and it would almost die, sometime it would, and then it would periodically surge between 500-700 rpms. Then it would run ok for a few minutes and then go back to running like crap again. I decided to take off the upper intake and clean it out as well as inspect the spider injectors for leaks. There was about 2mm of carbon and oil build up inside the intake. I detected no injector leaks. I then decided to remove the lower intake manifold in order to clean it as well. When I removed the lower intake manifold, I discovered something very odd...... I would have never guessed that after lifting out the lower intake I would find a piece of the roller rocker and the inside spring just sitting underneath the intake, also I discovered a push rod bent and "off its rocker" hahaha, I then realized that this had to be the culprit for why my Escalade has been running very touch since before I bought it. If anyone is having the same problem that persists after replacing everything I did before I found the problem, then hopefully this will help you! Have fun with it cause I'm 4 days into it and won't be done until tomorrow.