01' Cadi Seville STS NorthStar 4.6 loping idle

69000mi. Started by noting a loping idle when I pulled in garage. Drove to work next moring and Check engine light came on at one and only stop light on voyage. Engine Lopes about 100-200 rpm, runs smooth elsehwere. OBD Codes display 0171, 0174, fuel trim lean bank #1, 2. Replaced MAF-not the problem. Replaced Fuel Filter w/ injector cleaner-not the problem. Started and allowed engine to warm up, and then disconnected the low air flow idle valve plug. The loping immediately stopped. I removed the valve and inspected cleaned some carbon, but problem persists. Valve runs about $260, not sure if its getting a message to hunt-from vacuum leaks(Noted some good info on intake leaks in your columns-will inspect for tonight) or if you've ever heard of these motor valves binding up? Checked all vacuum lines and found no obvious cracks/leaks. Have heard that intake silencer can develop cracks-Any ideas on how to remove it(has one of those one time crimp clamps) and be able to reinstall.