95 Bonneville SSEi -hesitating at 38-46mph

[hofsgnx]

When driving my 95 Bonneville on a level surface at 38-46mph (constant speed, not accelerating or deccelerating) the car seems to hesitate or flutter slightly-the vacuum/boost gauge will fluctuate 2-3 lbs. It doesn't seem to affect the performance of the car when I floor it. The car pulls strong, starts good, just has this weird drivability problem. Car has 120,000 miles on it. Please note: anti-lock brake light and traction control light going on from time to time, however this driveabilty problem started long after that. The transmission/torque converter checked out fine. Recent tune-up did not solve problem. Help!

 

[SubZero350]

Sounds to me like if you are getting a TCS or ABS light there might be a wheel speed sensor problem. Being as your car is equipped with TC, this might be signalling your PCM to cut timing as a result of a perceved low-trac condition. This cut in timing can make a vacuum difference noticible on a gauge. My advice is to fix the known wrong issues with the vehicle before pursuing unknown causes. If there is a way to turn of your TCS, I suggest doing that to see if it has an affect on your stumble or miss. Do you have access to a scan tool? 95 computer systems have a "weak cylinder" feature much like the OBDII misfire diagnostic that will show up on a scan tool if there is a problem with the engine. I would try this if you have access to one.

 

[Hofman]

Good suggestions. Turned off the Traction Control and no noticeable change. I cannot imagine it is a weak cylinder because while it is "chugging" and you hit the gas, even just a little, the car snaps out of it. The "chugging" is the worst at a constant 41 mph. If you are going up and down even small hills you cannot tell, but if you hold it at a steady speed on flat road at 41 or so mph (steady speed of anything between 40 and 46) you can really sense the "chugging". Keep in mind when this car is at WOT it goes strong so I cannot imagine a weak cylinder. Any further input would be greatly appreciated.

 

[SubZero350]

i would like to know what your O2 mv are doing when this "chugging" is going on. Its a hunch, but perhaps you might have an O2 problem causing a lean misfire that you only feel when the TCC is locked up.