Thanks for the info. That is a good chart you have. I wonder if the dip from 19° to 18° is the knock sensor retarding the timing. Assuming that that year model the computer controls the retard and not the vacuum. I have been working a lot so I haven't had a chance to look at it any closer. It's also not my primary driver so I haven't been in a panic to fix it. I am borrowing a better timing light today so I will be able to get some better diagnostic info.