2000 Bonneville runs rough when cold

What were the plugs gapped at ? Check for loose vacuum hoses and electronic connections as well .

Buick 97 lesabre, runs rough when warm

Sounds like possibly more than on problem, crankshaft position sensor, or ignition module likely on starting prob which maybe affecting shifting due to hard code in ecm, or shift prob could be shift solenoid in valve body of transmission. Both parts readily available from local parts store

oxegen sensor?

Could be a problem with your intake air temp sensor or your coolant temp sensor. The most likely would be the coolant temp sensor. It may be reading cold and will make it run good as the engine is cold but as it warms it is not adjusting the air fuel ration to the proper levels making it run rough hot

Could be the fast idle sensor check to see that the vacume line is hooked up properly.

Remove your ignition module and take it to a parts house to be tested. This is common behavior for a failing module after it gets warm. Have them check it several times to insure it gets hot during testing.

leake intake manafold or bad vac line... try warm soapy water on running motor out of a spray bottle to find leak... the reason the censor seemed to hel is that the take time to set them selfs... after set back to square 1 leak in the air side of motor... typical in your car...

if u have a damaged plug it can be running on 1 less cylinder ,it will idle very rough,change it!

seem like you got the same problem as my scion xa, check the fuel pressure regulater. bad regulater some time smell like leak gas. auto zone might cause you about $80.00.