Generally speaking, I’m very pleased with the Vanden Plas. I’ve put a few thousand miles on it and it has returned a rock steady 23 MPG — overall. On the highway it gets very close to 30 MPG.
Two incidents have cropped up, one was a “check engine” light indicating (according to my scanner) that the secondary catalyst was under-performing. I cleared the code and it has not reappeared. The other is an ongoing issue which first cropped up about two weeks ago. The car developed a fairly severe misfire, running on five cylinders intermittently. Eventually it threw a code for “engine misfires out of range” or some such, with specifically “misfire on cylinder 3.” I replaced the plugs and the problem mostly went away, though it will still misfire occasionally at idle when warm. I suspect the coil pack on cylinder 3 is near the end of its life and the new plugs helped but didn’t solve the problem.
Coil packs are, sit down, $480 at the dealer (there are six on the car), but you can find them for about $190 each online. I think I will buy one and see if replacing cylinder 3’s pack completely cures the problem.
What was interesting was that the car didn’t throw a code until it was running very poorly indeed. Having a scanner and an OBD-II capable car is a different experience for me. There’s quite a bit you can learn from the port while the car’s running.