97 ASR Trouble Please help...purchase pending

[Schab]

Hi all,
I am new to the forum, and a pending 1st time Mercedes owner. My mother in law was planning on trading in her 1997 E420 over the next few days to get a new smaller C280. The car has 93,000 miles on it, always babied, dealer serviced and garage kept. When detailed, she looks brand new inside and out.
The only problem with the car is an ASR problem. For what the dealer is willing to give her on trade in, I see it as a sin to let the car go if this ASR can be fixed and would like to buy the car for myself.
The exact symptoms are: When stopped the ASR light illuminates, the engine revs up causing a lerching forward feeling. When you shut car off, restart it, it's fine again.

Could this be more trouble than it's worth?

Thanks in advance for the help!

Schab