what would cause the RPM to just suddenly jump while driving,?? any idea's

Its happen only on hway, I think it is not only the tachometer coz I feel the punch when its jump.
Is this something to do with tranny,TC or IAC.

Everything seems ok under the hood, no leaks, idle fine, no CEL.
Tranny fluids is ok (bit higher on high mark) changed recently.
I also clean the TB and PCV yesterday, but problem still there this morning.

Any one experience this?

 

At what speed does this happen ? If it's only at higher speed then the transmission lockup system is having a problem.

 

yes as this only happen on highway, i could say 80-100 kph.
if it is tranny lockup problem, please advice how could i deal with it.

 

Bring the car to a garage or dealer and have them scan for code, is there is something wrong with the lockup system, the computer should set a code for it. Could be just a solenoid, which can be change easily, could be converter it self which require the transmission removal, or hydraulic circuit inside the valve body which the tranny has to be open up. Could be some thing on the engine side that changing the engine load causing the tranny to come out of lock up.

 

It could be that you're driving right at the point where it wants to lock & unlock the torque converter. Say you go up a slight hill it unlocks, downhill it locks. It doesn't have to be a PROBLEM exactly. You're just noticing the transmission doing it's thing.

If it was a problem, it would display a flashing "D4" lamp. That's the transmission's version of a CEL.

 

Piggy: scanner of my friend didn't find anything, probably bec it clears all codes when i disconnect the battery terminal recently.
Jim: hopefully your right, however no flashing D4 yet.

i will change the oil once again this weekend and will see.

 

my 97 does that
it is the lockup torque converter
I notice mine mostly when the cruise control is on.
There is really nothing that needs to be done about it.

 

done with the oil change, so far so good, rpm is steady.