Cadillac: 1999 Catera idles rough, diagnostic scanner, vacuum system

Question
Hi Tom,
my wife's '99 Catera started idling rough about a month ago, most noticably after it has sat overnight or a long period of time. It had been purring like a kitten all along. The diagnostic computer shows that there is a misfire in cylinder 5. The check engine light is steady on. I took it to the dealer, they did a complete vacuum system flush, changed plugs and coil, flushed the injectors plus some other minor proceedures, all to no avail. Someone told me that the valves may need reseating, which sounds reasonable to me. Do you have any ideas on how to fix this without resorting to such an extensive (and expensive) measure? I am at my wits end, as the car sounds like an old truck now. Thanks for the help.

Answer
The diagnostic code must have been P0305 which requires the use of a diagnostic scanner to perform various test procedures.

If it is a valve problem have a compression test performed on the cylinder # 5 and compare it to the other cylinders.

Also have a LEAK DOWN test performed on cylinder # 5.

These tests require special tools and equipment.