98 bonneville running poorly

I'm working on a 98 bonneville with the 3.8 vin K motor in it. 66k miles I am experiencing a driveability problem... severe hesitation loss of power and bucking when accelerating. (cold or hot) under load only - when I rev the engine in park there is no missing or anything like that. About 3 weeks ago the engine light came on and my scan tool directed me to a misfire on #6... the #6 plug looked pretty black. I replaced the plugs and wires and the problem appeared to go away. now the same symptoms are back but no codes are setting.

I am also seeing a moderate loss in fuel economy. I checked all of the vacuum lines all appear ok.

I know the 3.8's are noted for bad intake manifolds - vacuum leaks developing over time due to warpage. Has anyone seen these type of symptoms with this problem? - is there any way to further diagnose this?

The only other thought I had was a bad MAP sensor

Any help would be appreciated.

Thanks

Dan

My 97 showed signs of this and we replaced all of the plug wires and the problem went away

Did you check the coil that feeds that cyl with a DVM, and for corrosive terminal?

You may also wanna check the injectors. Take out one of the plugs that you just recently put in and if there is build up on it, it is most likely injectors.