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started here sparks knock when driving now rough idle p0300 code

This is your first posting here, could you be clearer in your description, please.

This is a vague statement > started here sparks knock

A P0300 code indicates a misfire is taking place, this can be caused by a bad spark plug, a bad COP cassette, a bad injector or a mechanical problem hampering compression.

Don't assume it is bad, but 2000 COP cassette units have been known to cause misfires when they go bad. Swapping in a known good unit is a good way to diagnose one or if you had a spark detector.

If the engine has not been tuned up, plugs (100K miles), filters, etc, now might be a good time to see what is going on. You may be able to find a cop coil pack cassette in a scrap yard and use it to diagnose the condition of yours. You will need to get the correct bank, so it will need to be determined which bank is causing the problem. A good engine analyzer showing misfire counts should help to locate the misfiring cylinder(s)

Did you check for codes and post all here?

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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