odd highway RPM behaviour

[Foamy]

Well I have another question about my 99 SHO. Went on a road trip over the last 2 days to test out the new(used off ebay) throttle body. Well while driving with cruise on around 125kph I noticed that the motor would rev up anywhere from 100 to 400rpm then drop back down to normal with no speed increase. It would do this pretty frequently. Took the cruise off and drove it and found that if I let off the gas then get back on the gas it would rev up the same as it was doing with cruise on. That was on the way out, on the way back the car started to rev up at constant throttle(still no cruise on) and still a fairly frequently. When I got back into the city it would do the same thing at slower speeds but not as often.

I have also noticed that the car bucks/surges.stutters at slower constant driving speeds. Around 60kph I am barley touching the throttle and the car will stutter/surge/buck. As long as I am under very slight acceleration it is not there, but at constant light throttle it is very noticeable.

One last thing. Is it normal for the car to want shift into top gear with o/d asap? Again, if I let off the gas and get back on it at slower speeds(60kph again) it will rev up them shift into top gear causing the motor to lug around 1500rpm.

Thanks a lot for the help in advance. I am trying to learn as fast as I can so i can fix my own problems, but some things just confuse me.

 

[wymjym]

this should get you thinking

'Gen lll SHO 1996~1999

A neat feature of the T/C is the automatic lockup. In the AXOD-E/AX4S/AX4N, the automatic lockup is electronic and is controlled by the computer. It reduces slippage between the engine and transaxle which results in better fuel economy at highway speeds.

The T/C in the AXOD-E/AX4S/AX4N will lock up in third and fourth (Overdrive) at around 1500 RPMs. The lowest speed the T/C will lock up at is 30 MPH and the lowest speed it unlocks is at 25 MPH. If you're driving around the city and you release the gas pedal, it will automatically unlock. When it locks/unlocks, it will look like a shift on the tachometer, but you won't feel the harsh bump that's normally associated with a shift. The RPMs go up by about 500 RPMs when it unlocks, and the RPMs go down by 500 RPMs when it locks. This is normal. It will also unlock first before downshifting you add gas at cruising speed (such as going up a hill or want to pass another car) and lock back up after you get back to cruising speed. '

wj

 

[stripperking]

These are some of the exact sym. I was having. Read the post (Missing or serging up to about 70 mph) just a few posts down from this one. Has some good info on how to test tourque conv.