97 Bonneville with Surging problem.

Our Bonnie surges when your going down the road. Sometimes but not all the time. Say you have the cruise set and cliping along then suddenly..you can feel it surging. If you look down the rpms go up and down slightly. I'm not a mechanic but it does NOT feel like the torgue converter. I have had that goe out on a couple cars including a Bonnie but this is slower and not so pronounced as that. It does not "chatter". It is as if I were just moving the pedal up and down slightly as I drive along. sometimes it will just stop for a while and then start up later doing it. No service engine light. Runs great other than that. EXCEPT...it is getting horriable gas mileage. This is our 5th Bonneville and all have gotten way up in the 20's. Most very close and one even over 30 mpg on the highway. We just bought this one and it is only getting 19-21. Is that normal for the Series II? I have never had a car with the Series II in it. Our last one was a 94. If anyone has any ideas please let me know.
Rob

There are some GM service bulletins that may apply to your concern.
87-71-75 concerns problems with the valve body
00-07-30-002b references pressure control solenoid valve problems
both are for a surge condition

Rob, My 97 Bonneville had a similar prob a few years ago. The dealership replaced the valve body in the transmission. They had to put a scan tool in to look at this problem while I was driving the car. If you're getting 19-21 mpg combined gas mileage, that's about right for a series II. That is combined mpg., correct? Highway mpg could be as high as 27-28 mpg.

I will try to PM you with my specfics in a minute and thanks!

Also, yes 19-21 is some in town but mostly hwy driving. I just expected it to do as good as the others. I guess the Series II new and improved is not so improved huh?

Rob

I'm beginning to wonder if we should have kept the old 94 with 135k on it.

In reference to mileage, I just found the original sticker off my 97 SE. City MPG is 19, Highway MPG is 28. Then in finer print at bottom of sheet it calls out between 16 and 22 in the city, and between 23 and 33 on the highway. So, it does look like your mileage is low. Could there be ignition issues? Fuel mixture? Based on your mpg figures something doesn't appear right.

There are several possililities with the condition you describe. It is possible that an engine load condition is causing the convertor to "hunt." Fuel pressure conditions could be creating an unstable fuel delivery, including the possibility of a clogged fuel filter. Is the EGR valve operating correctly? Sluggish O2 sensors could also create this. The way you describe this problem precludes the possibility of electronic problems, which typically cause miss like conditions. Problems with a clogging catalytic convertor could also create this condition, as could unstable fuel chemistry, causing the knock sensor to operate excessively. Some food for thought: the computer, from time to time, will test the knock sensor and the EGR valve operation by creating the conditions which should cause knock, then "dither" the EGR valve to test its operation, watching the knock sensor's signals to confirm operation. It is doubtful here, however as this appears to be a new condition in your case. Since GM is constantly updating the software for its vehicles, you might also see if a software update has been distributed for this condition. You might switch to a different fuel source, in the event fuel chemistry is at fault. My experience has been that shopping for fuel has benefitted the performance of all of my vehicles, noticably. Some food for thought... Ray

Thanks for the post. I'm almost now convinced that it is the converter. When going down the road at a steady speed...like 70mph then when it starts to surge if I just touch the brake pedal to release the converter then the surging promptly stops and the the rpms raise from just above 2 to 3. GM merlin asked me to do this test but I have not heard back from him after telling him my results. But..I have a feeling it is something to do with the converter.
By the way, does anyone know if the oil pan will come off this 97 Bonneville 3800 series II without doing anything special? Will it just come off? My oil pan has been smashed a bit right where the plug is and it will not stop leaking at the plug. I'm afraid it is going to need a new oil pan. I've never done that before but I think I can do it myself as long as it will drop on it's own.
Rob

Sorry dude....sent you a PM...my bad

NO prob dude! You have been a GREAT help to me. I will have to have it looked at. Thanks again!
Rob

NO prob dude! You have been a GREAT help to me. I will have to have it looked at. Thanks again!
Rob

Just wanted to let anyone know that might read this. It was my converter kicking in and out in the tranny. They had to put a kit in the transmission and it cost us about $350 so it wasn't to bad I guess. Everything works perfectly now except the security light stays on a long time sometimes. It always starts though. Sometimes the light will stay on for 15 minutes.
Thanks for everyones help!
Rob

Howdy ... We have a 2002 Impala LS that is doing the same thing. This car has about 70K on it, and has the 3800 engine. I was doing a search and found this forum, looks like it's a wealth of information.

We just took a long trip, it was the first time I'd been in this car for a while but the wife had been complaining of an occasional surging problem. We've taken it in twice and nothing is showing up on diagnostics.

At 70 mph with the cruise on, a slight uphill grade will cause it to surge. The rpms jump 200-300 for a few seconds before it stops and settles in at the lower rpm. Steeper grades don't seem to cause this, and it doesn't happen at higher speeds (80+). But it does happen at lower speeds. It's always when under a light load, if you step on the gas a little harder it stops.

I got in the habit of downshifting to 3rd on this trip and that would stop the surging. At first I thought it was an electronic sensor problem, maybe the mass air flow sensor or the O2 sensor. But the more I think about it, I believe it's the lockup torque converter kicking in and out.

I have replaced the air and fuel filters, and checked for any obvious loose hoses, etc.

Any other ideas, before I take it in the third time?

Just wanted to let anyone know that might read this. It was my converter kicking in and out in the tranny. They had to put a kit in the transmission and it cost us about $350 so it wasn't to bad I guess. Everything works perfectly now except the security light stays on a long time sometimes. It always starts though. Sometimes the light will stay on for 15 minutes.
Thanks for everyones help!
Rob

Hi, I have read messages on this forum before, but this is the first time I registered. So I do not know if I will get this message sent in the proper direction.

I have my in-laws '97 Bonneville SSE. It is surging, similar to what is described from Rob. It surges at the RPM's when the torque converter should be locking inplace. It is worse with the A/C on.

What is the transmission kit mentioned above? I have put shift kits in transmissions before. Is this more involved than that?

Thank you,

mmnc

Hi, I have read messages on this forum before, but this is the first time I registered. So I do not know if I will get this message sent in the proper direction.

I have my in-laws '97 Bonneville SSE. It is surging, similar to what is described from Rob. It surges at the RPM's when the torque converter should be locking inplace. It is worse with the A/C on.

What is the transmission kit mentioned above? I have put shift kits in transmissions before. Is this more involved than that?

Thank you,

mmnc
I had the same symptoms with my 97 sse. I was convinced it was the converter. I found a post on this site suggesting a change of the plug wires. I questioned the advice but changed them and the plugs. The car now runs great with no trans problems or rpm fluctuations. Good luck.

Im new to this. Try some new plug wires and plugs. It worked on my car, with the same symptoms. Joe