Buick'* been acting strange for a while now without any codes..
Cleaned the IAC Wavering rpm at idle hmm.Step on gas up hill and it bogs down, had fuel filter bought..LOL.
Today I had enough & floored it, if it breaks oh well.
At about 4200 rpm it really bogged down & ding ding flash, Service Engine Soon Finally came on!
I hope it'* just the spark plug or wire on #6.... https://www.autoblog.com/2016/04/05/...fire-detected/

You can't feel a miss when it bogs? I think you have more than one problem.

I'm just curious. How long have you had your PA, how is the undercarriage (rust or rot) and how many miles (or kms) are on it?

Owned it 12 years, I'm the 2nd owner & It was an Arizona car, elderly driven with 78,000km on it. They moved to Canada west coast, & the car was too big for them, their loss my gain!
Those folks went though it all in the service Department, before selling it to me. New battery, brakes,& even new blend door actuators. Interior was perfect.
Undercarriage was mint, photo shows original condition.First thing was to Platinum Shield undercoat it.
Today it has 215,00 km on it.

Almost zero rust.The original muffler lasted 24 years, until a few weeks ago.

I always washed this car very well, including door jams,& lower panels.

The strange thing was you generally never felt a miss. Cruising on the hwy rpm around 1800 rpm it was fine.
Just a wandering rpm at idle was the clue something was up, & then going up hills it finally set the service soon with the 306 code.
I just checked my records, last spark plugs were now 7 years ago. Time really fly'* by.
It needs front brakes, tune up and new fuel filter installed. Will report back once it'* all sorted out.

That'* a good plan. It'* definitely a spark issue. The demand under high load going uphill requires more KV to set off ignition process. Plugs and wires will likely fix that. May fix the idle as well.

The gap had gotten a bit eaten away on cyl # 6, also very slight carbon fouling.
Instead of running these plugs for 70 k miles, I should change them sooner. NGK plug wires are fine.
For now all 3 of the rear plugs are changed. Will do the front 3 soon.
New fuel filter installed that probably made a difference too.

Power is restored, took it up to 4000 rpm up hill, no misfires now!
Rotors were shot, so all new front brakes. What a difference in stopping power.
Rear brakes wearing evenly are at 35% left.