Shudders at Idle/Previously It Had Power Loss

150K miles: I am the original owner, and the vehicle has been properly maintained. The only issue addressed in the past 10 years is the changing of the ignition coil and spark plugs at about 120K miles. Approximately 4 months ago, upon normal driving conditions I noticed an intermittent "ebb" of power quickly joined by flashing dash lights, then total loss of power. I had the vehicle towed to my mechanic who has conducted all work (besides pull-through oil changes), and he diagnosed problem and replaced alternator and battery.

About 10 days ago, I again felt the "ebb" of power just a couple of times, followed by 2 dash lights flashing; however, they flashed so fast I think it may have been seat belt and battery indicators, but I'm not certain. Fearing another loss of power due to previous issue, I was unwilling to drive the vehicle, and it was towed to the mechanic. He found the cable to the battery was loose, so he tightened it and checked other connections. As I drove it home from the mechanic's shop, I felt an "ebb" of power, the battery light flashed on and off quickly, and I began praying to make it 2 more miles to my home.

This time the mechanic came to my house and drove it back to his shop. They kept it 2 days and checked the charging system, belts, and the alternator fuse; however, all checked out fine, and they could not replicate the problem. I have driven it since with no issues.

Then yesterday, while the vehicle was stopped at a light, I noticed that while it idles smoothly and quietly (in fact, it seems eerily quiet), it "shudders" or "vibrates" every 30 seconds or so.

Background Issue: I don't know that's it's related, but everything is worth mentioning. For years, when the steering wheel tilt is adjusted, the headlight fuse blows.

When replying, please know that I am not mechanically inclined nor do I have knowledge of engines.