PROBLEM: My 1997 C280 keys would not turn the ignition, wheels were straight, steering wheel was locked with free play. Suspected a bad ignition tumbler. In 10 minutes it was fixed, didnt cost me a penny.
SOLUTION: Inserted, wiggled the spare key, tapped it gently with a leather mallet, and managed to gently turn the key to position one. I then rotated the collar 90 degrees counter clockwise and removed the ignition tumbler using needle nose pliers (make note of ignition orientation to reinstall it the way it came out)
You will see a number of moving brass lock plates in the tumbler that move inward when the key is inserted (these plates cause the problem, due to normal wear and tear, and wont retract all the way inward as they should). Simply pull these plates out with needle nose pliers, being careful to stick them onto a piece of tape in the correct order, should you want to place them back again (but why?). Problem solved. Reinsert tumbler and collar.
Good news is the car starts and I won't ever have a sticky tumbler. Not so good news is there is a potential issue of being able to start the car with a slim flat tip, however I tried that and it wouldnt start... apparently it still needs the key. In any case this serves as a solid temporary fix IF you want a new ignition at a later date. Personally... I'm doing without a new tumbler, deciding to save $1000 bucks (what Mercedes quoted me for a new one installed by them).
Secondly, as happened with me, if the engine won't start after you reinstall the ignition, most likely the anti theft feature was activated. To deactivate, close the doors, then lock the doors with the remote, then unlock. That resets the anti theft... and the car will start.
Hope this helps.

I don't blame you one bit. It's just an old W202 that won't ever be worth anything, so who cares if you pull the tumblers. Anti-theft won't be a worry because honestly, who is going to want to steal it?

__________________
'80 300SD - '83 240D - '00 E55 AMG - '02 G500

lol. to be honest.... the new generation of car thiefs would never know. But... if you are dissing the true value of a W202 mercedes... then you are clueless.

I have this same car. The key has a RFID chip so even if the ignition is turned with a screw driver, the car will only run for 3 seconds.

As for the W202 , it is more 'funner to drive on twisty roads than my 97 SL320. The SL is more of a distance highway car.

Interesting on the RFID CHIP... are you sure about that for a 97? I can use the spare with no issues, I am pretty sure it doesnt have RFID. Im with you on the funner to drive.... I love how it hugs the road and turns on a dime.

Yep, 97 was the first year for the RFID chip key for the W202 , W210 and R129. What is your build date?

You should have a black / chrome antenna ring around the ignition lock, the has a small black wire that leads to a 3 x 4" black box behind the instrument cluster. This box reads the key then sends a message to the engine computer to let the car run. The chip key / black box and engine computer are all programmed together, swap one and the car won't continue to run.

Also know, a new code gets written into the key after each start attempt. A weak cranking battery can disrupt the write sequence and that key will no longer work.

The black box looks like this, the chip in the remote fob is a PCF7935. If you have a non remote valet or clipped head pocket key, they also have a chip.

Attached Thumbnails

 

Thanks 97! Its always good to learn something new about these cars... I know exactly what you are referring to... I saw that wire around the fitting just as you described. Explains why the screwdriver wouldnt crank it over. Makes me wonder why even have a tumbler.