Weird problem while cruising on freeway

[95Batmobile]

Sometimes when I'm just cruising on the freeway, my RPMs start bouncing up and down. The car is acting as if it wants to upshift or something, it just hops up and down by like 500 or 800 rpm and doesn't stop until I let off the gas or give it more. It doesn't do it all the time, just at random times.
I replaced my plugs a little while ago, but I havn't done anything else as far as coils or ignition or anything. The check enginge light doesn't come on either.
Any suggestions?

[Tri-Flo 99]

if your cruise control is on, it could be your converter unlocking and relocking...i dont know though

[95Batmobile]

I Don't use the cruise control...

[pvtschultz]

If you are doing low RPM cruizing, mine seems to do it at around 50-55 when I try to accelerate with it in 4th great. The torque converter can't decide if it wants to unlock for the acceleration. I just tap the gas quick to unlock it, get off it a little, and then back on while the converter is still unlocked.

If you are letting off of the gas to slow down, and then getting back on, the converter unlocks when you get out of the gas (better gas milage) and then when you get back into the gas, it will then lock giving you a substantial RPM drop. Comparably speaking, for engines with a lot more torque, the converters are a lot tighter. My old bomber Impala would only flash to around 1200 RPMs or so. The 'bird will flash way past 1500, but the lockup makes up for it.

Hope that helps

[95Batmobile]

It usually happens when I'm going home... which is why I'm crusing at about 85-95mph.
If its just the converter then there isn't really a problem, I just need to keep doing what I have been and just give it some gas or let out?

[Devilboy28]

Fuel filter?? Mine acted up once and that was the cause.

[Magnus]

Hmm... problem diagnosis and power loss qeustions belong in genera tehc.. i'm moving this one there.

[morbid]

maybe your throttle position sensor is starting to go out?

[sped214]

I had the same problem in my 97. A buddy at a shop got to looking, and found a TSB that addressed this issue directly. It's a problem with the PCM programming and the TCC engaging/disengaging. He downloaded the updated and flashed my PCM. This was about 6 months ago, and I haven't had the problem since. I can't remember the TSB number, though...

[Takumi Fujiwara]

yeah, for me this happens around 1k- 1.3k rpm. AS many people have said the idea of firebird automatic overdrive, to me it seems like its fickle and not picking a gear, it just bounces until i gas it ( downshifting ) or left off, ( upshifting ) to me its jsut the sweet spot in the tranny bur the pcm code seems resonalb.e

[sped214]

It was right about 2k for me, in OD. I usually saw it going up a slight hill without giving it a lot of gas. It occasionally happened driving in town just before the D to OD shift (42-45 mph). I wish I could find the TSB...

[Guardsman]

It may also be the TCC apply valve. There is a TSB for a known problem withthe valve body. The 95 and up cars use a variable pressure TCC apply valve (it's basically to make soft tcc applies for joe public). Over time, the valve will start to leak, and it can't get enough pressure up to keep the tcc engaged (the rpm changes).
You may have another problem that's related, at low speed and part throttle, shifts from 1st to 2nd gear will be really hard, i.e., like you got rear-ended hard. That's the result of the fluid heating up because the tcc is only partially engaged, and the PCM detects the high heat, and the inability of the tcc to engage, and commands maximum line pressure in the tranny.
Anyhow, a couple of companies make a fix kit that changes the tcc apply valve from the variable pressure to a straight on/off apply. Check with a good tranny shop, they should know how to find it.