2004 Chrysler Sebring slight misfire and vibration

Hello and thanks for taking the time to look at my post. I currently have a 2004 Chrysler Sebring in my shop with a 2.4L DOHC with 85,000 miles and an automatic transmission. It has a slight vibration at idle (both in park/neutral and in drive). It also has a very slight intermittent misfire… maybe one every 10 or 20 seconds. There are no error codes. I have already eliminated mounts, coil, cam sensor, plugs, wires, compression, timing. All of those have been tested and/or replaced. All fluids are at the right level and are in good condition. I own a small independent repair shop and have quite an array of tools and scanners. Saying this, we are stumped! I really think I need to look “out of the box” on this one. If anyone has any ideas on this or has experienced anything similar in the past, please let me know. Luckily, this is a personal vehicle so I don’t have an angry customer here and time is not an issue. Thanks in advance!