I had the same problem in the same car. In my case it was a bad EIS. That is about a $1500 job at the dealer since you have to get new keys also. I think I had a thread on here about that.

Another person said they fixed theirs with new keys and that thread is around also. That will still cost you about $300 per key, and the computers can only accept so many new keys then you have to buy a new one.

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra