A bit lengthy, but please read/suggest if you have any assistance to offer!!!!

My ’02 CLK430 had sat idle for 2 or 3 days. Went down to start it, she turned over just fine, idled, and then died about 3 seconds later. Tried again, this time the key would go to position 2, but would not engage the starter at all when turned to start. Hmmm…pulled the key out, tried to put it back in, the car would not accept the key at all. Tried to open the trunk, key no longer opens the trunk, or locks/unlocks doors. Used the key insert to manually open the trunk to see if the battery connection was bad. Perhaps the negative terminal was a bit loose. Disconnected/reconnected, key still won’t accept the key (by ‘accept’, I mean when you place the key in the ‘socket’ the vehicle grabs/locks in the key so you can turn it). Note: the dash and interior lights were on just fine, though after a few more tries, everything was dead.

Had to have the car towed to a shop. She gets there, starts up just fine right away off the truck. The shop said the negative battery terminal connection was loose, though it may likely be issues with wiring aftermarket stereo equipment (amp) in the trunk. Picked up the car from the shop, drove it around town, ran some errands, it’s all good. Go to leave for vacation, drive out of my lot, park it to grab the last item of luggage, car doesn’t start up. Had to have the MB roadside assistance give a jump. I drove it 90 miles just fine, parked it for a week, started it up just fine, and drove the 90 miles back home. I’m waiting for an appointment with a trusted local stereo/electronics shop to have a look as the previous owner I could tell had some aftermarket equipment installed (I could see a sub controller was still in place when purchased), though the supporting equipment had been removed (i.e. sock stereo in place, no extra amp, subs, etc – though I’m not sure if he botched any wiring in the previous owner’s install).

Note: The alternator is 6 months old, battery 3 months, MAF less than a year. Car reads no errors, MB tech that came out read that the alternator is working/charging properly. Until this issue, I’ve had some maintenance done on the car that the previous owner had not done – gaskets, brakes, etc – and she runs as if just off the lot. No problems.

Please help! I’m at a complete loss.

 

I've found some forums about a bad K40 relay, but that only seems to be a possible solution if the initial start, then shut off were the issue; nothing about the subsequent problems. If it's any help, the car has 50k miles on it (not bad for a 10 year old car), though much of the neglect the previous owner inflicted seems to be by leaving it outside in extreme heat for some length of time (Some components seem to be accelerated in age due to weather, debris, etc).

 

Ugh...150+ views and no bites.

 

I just had my 05 CLK55 Start up fine and while idle stalled. It refused to start, just kept cranking. after I called a tow truck I decided to try one last time to get it to start and it turned right on, I then drove it to my local dealership and the MB Tech showed me that I had a bad crankshaft sensor, and driverside gasket leak. From what I remember the sensor could not find the valves in order and thus wouldn't let the car start.
I shouldn't have made it to the dealership which was 30 miles away but I somehow did.

Dont know if your car may have the same issue but you never know.
Could be that you may need your key reprogrammed for the car.

 

One of my keys is new from the dealer (~1 year old), the other is original. Both work or don't work in similar fashion as one another based on the car's "mood."

No certain about the sensor - most of the time mine either cranks and turns over just fine, or locks out from even being able to crank (acts as if the battery is dead).

 

It sounds like you've ruled the keys out but I had a similar issue and it ended up being the keys. The key would go in but the interlock wouldn't disengage for me to turn the key. I'd give it a few minutes try again and I'd be fine. It took about two months of this as it got worse and worse and I finally had to tow it one day. Dropped off at the shop and wouldn't you know it started just fine. I only have one key so I got it replaced at my technician's advice and haven't had a problem since. Keys take a beating, so with the sensitive electronics it's no wonder they go bad after awhile.

Do you have the emergency slim key?

 

I do have both slim keys for the original and new (1 year old) key. I can get into the trunk/doors just fine it's just the above symptoms which are puzzling. I just find it hard to believe both keys could be bad at the exact same time.