'97 Avalon - ABS and 'trac off' warning lights / rough idle

Hi,
A couple of times now we've seen the 'ABS' light come on in our '97 Avalon, accompanied by a flashing 'trac off' light - it did it once
yesterday, then once again today.
Both times, the car has continued to operate normally without any obvious braking/handling problems - until the engine is switched off and restarted. At that point, the ABS and trac lights clear, but the clock on the dash resets and the engine struggles to hold idle (although the car's perfectly driveable). After a subsequent restart, everything's fine - no warning lights, no idle problems.
It's icy and snowy up here right now, but it wasn't exceptionally cold on the two times this has happened (i.e. the car's been fine when it's been much colder). A few miles prior to this happening the first time though I did clear snow and ice build-up from the passenger-side front and rear wheel-wells; I wonder if I dislodged a sensor wire such that it's now making intermittent contact? (OTOH, the car's got just short of 200k miles on the clock, so it's probably long overdue a few failures :-)
Oh, both times the lights have only appeared when pulling away and making right-hand turns - that's probably simple coincidence, but I figured I'd mention it.
I'll dig around behind the wheels later and take a look for any obvious damage (should have done that before posting, I know!) but are there any other obvious things I should be checking? Is the frequency of the trac light flashing significant? What about the time reset and rough idle? That just seems odd, like a computer glitch rather than braking system fault...
cheers
Jules
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Like Hachiroku says, check the battery ground connection first, and after you get that fixed, pull trouble codes for the ABS the next time the lights come on and report here.
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Ray O
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