2000 Blazer RPMs jumping up and down at steady cruising speeds
 

2000 Blazer ZR2 4X4 auto 225000 miles.
I picked this Blazer up a few weeks ago. Didn't seem to have any issues other than being a bit sluggish, so performed some routine maintanence as ritual with every new-to-me vehicle.. Removed and thoroughly cleaned throttle body and IAC. Cleaned MAF with electronic cleaner. Replaced fuel filter and PCV. Oil changed with 10w-30 maxlife synthetic blend..
Now starts up great and idles around 600-700.
a few days after doing all this, I noticed when cruising at any RPMs between 1k - 2k, the tach jumps up and down and loses power until I accelerate over 2k or let my foot off the gas. The speed or gear doesnt seem to affect this, as long as I'm in that range of RPMs, it fluctuates and seems like it's struggling.
I'm new to the whole spider assembly thing, could that be it? Seems like it would do it all the time if that was the culprit.
waiting on new plugs in the mail, anything I should check before I rule those out?
No check engine light and no visible leaks..
thanks!!

TL;DR:
RPMs fluctuate between 1k-2k when cruising.

i forgot to mention in the first post, I searched around for solutions and though maybe it was the TPS as others have suggested in older threads.
i checked the voltage of the TPS, sure enough, spiked around 3.5 volts. Replaced with a BWD sensor. Voltage checked out fine. However it's still having the same exact problem.

If this problem starts at exactly 46 mph (and above, in 4th gear) it is the torque converter clutch connecting and disconnecting. If this is what is happening, we can discuss more.

Yes, it is when going between 40 - 60. So what does this mean?

Okay, I've looked into the TCC Solenoid problems. Not a biggie since I was already going to do a filter and gasket change.
shopping for new TCC Solenoids, I see i can get an ACDELCO kit for about $130, which includes:
2 Shift Solenoids - A & B
Epc / Force Motor - Pressure Control
3-2 Downshift - Pwm Solenoid
Pressure Manifold Switch - PSM
Tcc / Lock-Up Solenoid
Internal Harness with External Case Connector

Should I replace those things while I'm in there, or just get the TCC Solenoid? I dont mind paying the extra $100 if i dont have to open it again (other than semi-regular ATF changes) and help extend the tranny life, but I also don't want to replace what's not broken and end up breaking something, lol.
what do you think?

Hold up there cowboy! Don't start jumping to conclusions. Could be perfectly normal or could be poor engine performance as well. Post video of your tach and speedo during this problem and we can discuss more.

The video isnt great but its hard to mimic the problem in traffic, lol.
In the last few seonds of video, you can see im going about 45 mph with my foot slightly on the pedal and it starts surging
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edit: forgot to actually post the video
https://youtu.be/g7K7ZJ8HU_w

its only 25 seconds

Thanks for the video. I wanted to make sure it wasn't normal TCC operation. It's not normal TCC operation. And you say it will do this in first or second gear as well, in the same RPM range? If so, it would seem the engine itself is surging dramatically and you will need to deal with engine performance.


But if only doing this surging in high gear, then I would suspect a possible trans problem of some sort. I'm not a tranny man. My tach was doing a few hundred RPM dance for a few weeks when my trans was getting ready to go last time, but only at steady speed and 50 mph with TCC engaged. Was not as severe as yours. Above 55 or below 50 and no problems. As I understand it, I eventually ended up with so much 3-4 clutch material in the pan that intake screen was blocked and pump started howling and it left me sitting at the side of the road. Let it sit for a few minutes and stuff would fall off and vehicle would move again. They completely rebuilt it and put in a new converter (and it was on their dime under warranty).

Hmmm.. well that worries me. Thanks for your input. My tranny does some other weird stuff too. Like accelerating quickly onto the freeway, for example, RPMs would be a steady rise, then out of nowhere, jump to like 4k. It pretty much does this for 3rd and 4th.
i dont know.. i'm not a transmission guy either. I worked as a GM tech a few years back and saw 'em getting disassembled all day, but I never touched 'em or paid attention. Quit my apprenticeship (regrettably. I'm fairly young, obviously) and decided to just keep automotive as a hobby and side business.
well, if a TCC solenoid, boost valve and fluid flush doesnt fix it, time to start reading up on rebuilds and go pull one from the yard to start working on.

Oh, and when i initially posted the thread, I hadn't been experiencing the issue long enough to know exactly when it occurs. It's always when steadily cruising at 40-60 mph, 1.2k-1.8k rpms. Never below those speeds..