I had the same problem with my 300E. There is a coolant temperature sensor at the end of the engineblock (at the firewall) with a two-pole connector on top of it. One wire is going to the computer (behind the battery), the other leads to the EZL controlunit on the left front fender.
It is a resistor changing its resistance according to the coolant temperature. If I am not mistaken the warmer the engine the lower the resistance (I don't have the manual with me but it list the actual values.)All you need is an ohm-meter to test it. Check the resistance to ground on both poles. The value should be same for both. If it is infinite there is your problem. The sensor is under $100.00 and easy to change. By the way, the shop that changed the voltage regulator, stay far away from those kind of people. That regulator should be somewhere around $50.00 and takes about 10 minutes to change on the 103 engine and the alternator stays in place. I am just wondering how they came to the conclusion that the cold-starting problem is caused by a bad voltage regulator?? The cold start injector is at the middle of the block (between the 3rd and 4th injector) with an electric connector and a fuelline attached to it, but you have to remove the airfilter-housing to access it. When I had the starting problem I simply supplied battery voltage to it and I could hear it spraying fuel so it was OK. By the way the Partsshop sells the manual on CD. I think it is worth the investment if you are a do-it-yourself type.
The ignition-coil is the same for the 4 and the 6 cylinder engine so you can put in a used one from a 190 as well (this is according to my Mercedes engine manual). I got mine for $40.00 off of a 190 last year and it is working like a charm. I don't think your engine will start if you have a bad coil. Mine didn't anyway. And the engine manual walks you through the procedure to check that coil.
Good luck.

Alex

[Edited by dacia on 03-15-2001 at 05:48 PM]