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What causes a car engine to idle rough and miss?

This car is a V8, always serviced

Plugs and wires changed, O2 sensor changed, distributor new, premium gas used, injector cleaner used – still rough idle and miss Thanks!

Any ideas? 1990 Cadillac 4.5 liter 99K

I’m assuming a new cap and rotor were part of the distributor replacement.

Has a compression check been performed? Perhaps one of the valves is burned or not sealing properly.

When was the last time the fuel filter was replaced.

Compression test.
Check for leaky EGR valve.

Look for vacuum leak