Are you ready for the new puzzler?

There was this fellow. And this fellow had let's say a 1985 Nissan Sentra. The car is unimportant. It just happened to be a Nissan Sentra, but it could be anything. And his problem was that he had a noisy valve. So being a do-it-yourselfer of sorts, he decided to adjust his valves. And he removed the valve covers and adjusted the valves. So he puts the valve cover back on. And with great anticipation, he starts the engine and it's still clicking and ticking.

So the next day he takes it to his mechanic. His mechanic says, "You obviously screwed it up. You need a valve adjustment." So the mechanic adjusts the valves. They start up the engine and tick tick tick tick. Kind of like a time bomb.

So the mechanics says, "Oh, you just need a camshaft." And the fellow says, "No, I'm not going to do the camshaft and I'm going to wait until it gets worse. What's the worst that can happen? It chews up the camshaft even more. In which case I'll still need a new camshaft."

So the noise goes along like this for several months. Three months later, he takes the car for a tune-up. They tune the car up. He drives it home and he realizes halfway home that the noise is gone. It just took him a while to realize it.

What happened?

He called them up. In fact, he said, "What did you do to my car? Did you adjust my valves?"

And they said, "We didn't adjust no stinking valves!"

So the question is, how did a tuneup solve this problem?