700R4 TCC Solenoid bad? (limited EFI content)

[Peter Gargano <peter@ntserver.techedge.com.au>]

My VN Commodore 3.8 V6 has a "Turbo Hydra-Matic 700R4" and has just 
one ECM connection - the TCC Solenoid (I'm sure this isn't news to most 
list members ;-) I had to look at my manual!...

My wife mostly drives the VN to work in light traffic. I only get to drive it 
when it's playing up, or on a long trip. Last weekend the car (apparently)
had a problem with unlocking the TCC. When doing constant freeway speed (say
~ 70 mph) and coming to a hill, there would be a point when you'd expect 
the TCC to unlock to get a few more revs (and torque) to make it up the
hill. At this point the transmission seemed to try to unlock and immediately
lock up again, causing an oscillation at about 3-5 Hz - only cure was to change
back to 3rd (from OD to D on shifter) until over the hill!

I swapped the ECU and this didn't make any difference - haven't had time to
check anything else (wife has car!). I'll swap/check the TCC solenoid tonight:

It seems like the TCC solenoid may be pulling in and then almost immediately
letting go - is this common, or do I have a hydraulic (ie. auto trans) fault?

Note that this problem is not apparent when accelerating (fast or slow) up in
the gears, only when the motor/ECU/transmission senses a load that would cause
a downchange/TCC unlock condition.

All ideas greatly appreciated.

regards, PG
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