2004 Tahoe Z71 144,000 miles. Engine would develop a knock or slap after revving over 2,500 RPM or so. I researched and found various suggestions. Tried fuel additives, oil additives and was going to take to a mechanic. I found one thread that said it could be carbon build up. Bought Seafoam intake spray and tried it. At first, engine wouldn't remain idle when intake tube was removed. It wouldn't start with tube off either. I put the intake tube back on, had my daughter start it and had her maintain 2,500 RPM. I backed the tube off slightly and began spraying the Seafoam. We shut off the engine and let it sit for about 15 minutes. The video below shows us starting it and revving it up. The knock is loud at the beginning and after two minutes, the knock is gone. I drove it 80 hard miles since and knock hasn't returned. It also will remain idle now when intake tube is taken off.
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