OK, I'll add my 2 cents worth.

You mentioned that you might have switched some spark plug wires around. If so, did it backfire? If it did, then you may have caused a vacuum hose to come off in the Idle Control Valve area. Check all hoses going to and from the Idle Control Valve, and verify that the spark plug wires are in proper firing order.

I've seen this happen where the vacuum hose popped off at the bottom of the air/throttle body location. The engine would not start, plugged the hose back in and the car started right up.

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible