This is the condensed version of my story:

Car is 1998 C230

Original problem is intermittent failure of EIS to unlock: Sometimes I would insert the key and the steering wheel would NOT unlock and the key would NOT turn. However, if it turned it would start right up. All other functions of the key always worked fine. Two different keys had the exact same result so concluded it was a bad EIS.

I sent the EIS and 1 key to a person to be repaired. First they said they could not fix it, then they said it was fixed and they returned it with the key.

I put it in the car and now the symptom is: Everything works fine, the steering wheel unlocks and the key turns every time. BUT, the starter will only run for 1 second then stops and the car never starts.

I really don't know what to do at this point. I think the ECU does not like the EIS anymore (or the key) due to something the repair guy did, but he will not say what he did or didn't do. He just says it is the fault of my car even though my car never ever had that symptom before he fixed the EIS.

Anyone know any EIS experts?

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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

I'm only minorly familiar with the EIS on my 99 C230 parts car.

First think I'd do is remove the bolt from the steering column lock. This way if a total failure occurs you won't have to cut things apart.

I'm talking about the box on the left lower portion of column, under dash. Insert the key, wait for the ZZZttt noise of the column unlocking, remove the 10 mm headed nut then push the bolt up and out. This bolt is trapped when the column is locked. You can either zip tie around the box / column or pull it back and zip tie to something else. Be sure not to let the wires flex or be under strain.

Open the computer box on right side of under hood, near windshield. There should be a large purple ( color I think ) wire in a 8 or so wire connector that plugs into a rectangular relay that has 5 or so fuses on the top. Put a test light on this wire and turn key to start confirming that is the wire. With the key in the run position I'd apply 12V to the purple wire and see if the engine runs.

What is your reasoning on this? I am willing to try it but I believe the immobilizer is being activated which will cut off fuel as well.

__________________
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

This is to determine if there is a starter circuit problem rather than a EIS / anti theft problem. Starter circuit as in from starter all the way back to the ignition switch.

I'd need to see a wiring diagram but I'm pretty sure the starter circuit is just a set of contacts in the EIS ( where the key goes in ) just like a regular ignition switch.