So is the surging trans related or engine/emissions/fuel/electrical issues?
Describe exact issues, at what temp (engine, ambient and trans if possible), road grade, throttle position etc.
Bill MacLeod, I guess that is what I am uncertain of.
When I had the first CEL/Limp mode and the RPM surge with the torque converter rumble, I initially and instantly thought it was transmission issue. I had the transmission serviced (pan dropped/filter replaced/fluid replaced) by a trusted local shop, with some mechanics that my wife and I are friends with and that I've been using for 3-4 years now. At the time I cross referenced the materials they used to be correct (I don't know off the top of my head, but I'll dig up the paper work later). This transmission service didn't do anything as I pulled away from their lot. Driving it for a bit more (10-20ish miles?) the torque converter rumble dissipated, but the RPM surge continued on. Fearing the worst I took it to a reputable local transmission shop that has been in business probably longer than I am alive. A specialist hooked it up to a scanner and took it on a test drive. When he got back he said it had no stored codes, it threw no current codes, and he couldn't detect anything out of the ordinary - BUT, he said it most certainly had some sort of RPM fluctuation and wasn't sure if it was directly related to the transmission. He further went on to say that a variation in the RPM like that should have threw a code of some sort.
So, that is when I switched my focus from a transmission related problem to an engine/emissions/fuel/electrical problem. I was basically taking wild stabs in the dark to solve the issue (well I guess you could say they were somewhat educated assumptions).
The RPM surge seems to happen like this -
I start the car, let it warm up a minute or two. Upon the very first trip of the day, I'll get it up into the RPM surge zone of 35-45MPH with no problems. After about 5-10 minutes of driving in town, I'll get into that zone again and the RPM surge will begin to happen.
How this happens is:
1) I start off by going through 1st, 2nd and gears to about 35MPH, which is the speed limit on most of the roads near me (35, 40MPH).
2) The transmission will shift into 3rd gear, RPMs drop to about 1-1,500 RPMs and I ease off the accelerator to remain at speed limit speeds.
3) When it shifts into this zone the RPMs will begin to pulse/surge by going up maybe 100 RPM more and cycle through - so it will go up 100 RPM, then drop down 100 RPM. It seems to alternate every second, so 1 second it will be up 100 RPM, then next second it drops down 100 RPM. This happens on flat roads, hilly roads, doesn't matter. The only time it seems to not do it is when I'm going down a hill, but normally that is because I let off the accelerator all together. Given a long enough road, I think this would go on indefinitely.
So - road grade is either up hill or flat, it has been happening at all temps this winter (below freezing, above freezing, near 60-70 degrees etc...), throttle position is when I am staying at a steady speed (basically just resting my foot on the pedal to keep it at 35-40mph). I have no clue about the transmission temperatures, but it seems like it will be fine on the first few minutes of a trip, but then after that it will continue to do it no matter how long I've been driving.
To eliminate the RPM surge I either give it more gas (or switch out the O/D) to bring the RPMs up into the 2-3k area (or it shifts into the next gear), let off the accelerator all together, or slow down/apply the brakes to get out of that zone. Sometimes if I'm on a flat road and it begins to RPM surge, followed by the road beginning to go into a steady incline, the RPM surge really bogs down and the PCM seems to really resist shifting into a lower gear.
I'll see if I can get more specific about things... maybe I should just create a video also.