I'm thinking of buying a used 2006 Volkswagen Jetta. It has a 1.5 liter 20 valve engine, and I really don't know what that means. That's good, right?

And is this a good used car to buy?

Are you sure its a 1.5 liter 20 valve engine? Jetta's of that year came with a 2.5 liter 5 cylinder engine (which would have 20 valves, 4 valves per cylinder.) Basically what valves do is some open to allow air to enter the cylinder, and then some open to allow the combusted mixture of air/fuel to exit. Most vehicles (to my knowledge) have four valves per cylinder nowadays, I know it was less in the past, but I think just about all have four valves per cylinder now. Five cylinders is just one more than four, one less than six.

Oh, and Jetta's are actually quite nice vehicles. I would definitely pick one up if I were in the market for a used car, and found one at a decent price.