I have a 2000 SSEI Bonniville with 103,000 miles on it. Under steady accelerations when the boost gauge gets to 1 to 2 positive pressure the power starts to pulse or cut out at a steady frequency and the amplitude of the surging increases to the point where the car develops a buck if i leave it in the 1 to 2 positive boost range. Increasing or decreasing accelration to get the boost out of the 1 to 2 +PSI range will stop the anomally and the car seems to run fine. Usually i let off the gas and accelerate at a different rate but by this time i am usually about up to the hiway speed i want to be at. The car has done this since i purchased it with 80K miles on it. There are no check engine lights. There is a miss at idle meaning it seems to idle fine for a couple seconds then miss. I have not taken the car to the dealer and would rather not. I have access to extra used sensors from parting one of these cars out to help troubleshoot but havent really tried anything as I am thinking it may be vacuum related. Would like someone help with possible cause of the problem.
Thanks

Welcome to the site!

Welcome to the forum!

I moved your post to the mechanical section for better visibility by our gearheads. They don't always see the introduction threads.

Could be your O2 sensor, or a dirty MAF, try unplugging the MAF and see if that corrects the problem. Could also be the EGR pintle stuck open.

I am having the same issue, and am starting to believe it is transmission related. Accelerate aggressively and there is no issue. It kicks down a gear and away we go. Under mild acceleration its almost like the tranmission can't decide whether to maintain the current gear or kick down a gear, and it results in the symptoms you describe.

Before I take it to a friend who knows transmissions better than I do, I am going to try reset the adaptive learning by disconnecting the battery overnight. Next step is to change the oil and filter on the transmission. If those don't work, I will take it to my friend to look at.

Could be engine, but I have a feeling it is transmission.

I believe it is engine related because the tachometer oscilates 300 to 400 RPM when this occurs.

Transmission speed and engine RPM'* are directly linked. You could be correct in your assumption it is an engine issue, but I would not rule out the transmission.

in my best opinion im gonna go with fuel pressure , possible weak fuel pump same thing happened to me on a older gtp was fuel pump

Hi, I ran into this problem on my 2000 SSEI. Turns out the TPS ( throttle Position sensor) had a bad spot in it were it would give erratic values and confused the transmission. My transmission guy actually helped me find the problem.

A very similar thing happens in my 98 SSEi. While cruising through 50-60 mph and I get up to about 2lbs of boost, the car has this back and forth buck until I let off the gas.

Do you also get the problem driving up a hill or in cruise control?

I asked around here and the main consensus was to change out the spark plugs and ignition wires. I haven't had a chance to do it yet but when I do i will let you know results.