2003 Mercedes CLK 430 problems

My mom just picked up a CLK 430. I drove it around for a bit and noticed that a few things didn’t seem quite right

  1. The transmission seems to start out in 2nd gear rather than first even when the transmission is not in “winter” mode. The transmission is also very hesitant to downshift, and often times will not downshift at all if the car is moving.

  2. There’s a noticeable amount of lag time between when you stand on the gas and when car actually starts accelerating.

  3. The engine doesn’t seem to rev very quickly or freely, and there is some noticeable pinging when the engine is under load. Performance was very tepid for a 275 HP car.

The spark plugs and ignition wires were replaced last week. The car has 105k miles on it. I know the previous owner used regular unleaded, and the owners specifically states that 91 octane should be used and goes as far as to mention precautions that should be taken should regular unleaded. The car was filled up with 93 octane fuel earlier today.

Just 15 minutes ago, I took my stepdad out in the car to demonstrate my findings. On the first drive (about 5-10 minutes) the car acted like it did when I had driven it earlier in the day (not downshifting, hesitating, lack of power, etc.), and the check engine light came on. He wanted to drive the car to see for himself. So we pulled over, shut off the engine and switched seats. He got behind the wheel, started the car, the check engine light is still on. But the car ran perfectly. It was starting out from 1st gear and would downshift promptly when give full throttle. Performance was immensely improved. The check engine light is still on though. The car has a 1 year bumper to bumper warranty. So I guess they can bring it in to have it looked at.

I’m just sort of at a loss as to why the car performed so poorly when I drove it, and all of a sudden performed correctly, after the engine was restarted. Anybody have any ideas about what happened?

At least you’ve got the CEL to start with. I’m no Mercedes expert, but I’ve often heard of their sloooow throttle response and 2nd gear starts. But the CEL points to a problem somewhere…

I read a lot on the internet, and looking at the problem my first question is does winter mode influence downshifting, In my mind that would be a good idea to not have downshifting occurring on wintery roads. The most common issue seemed to be a software upgrade. One note I saw was to never change the mode unless you are in park. Then there were a plethora of minor fixes to varied to be off much help. Does the Bumper to Bumper include software upgrades?

Could it be a holdover from the 87 octane gasoline? If the car has to change timing to accommodate high test, this could take a little time. The CEL won’t go out for a few drive cycles, as you know. Since this is a cheap fix, I’ll hope for it to work. Maybe Mom can drive ti around for a few days to see if the change for the better is permanent.

@FoDaddy I worked at a Benz dealer for many years. Your transmission will start off in 2nd gear, unless you force the downshift. That is the way they’re programmed to operate.
Please post the fault codes.
The 113 engine (your V8 was well known for having faulty MAF sensors. This would usually result in fault codes. Some people swore by cleaning them, but I always felt more comfortable replacing the part.
Did you put in the OEM plugs. Those 113 engines often didn’t like the "wrong’ plug.

I suggest you bring the car to a shop with a scanner that will retrieve all the Mercedes-Benz data and codes, not just the generic OBD 2 data. There are many functional tests and PIDs that many of the aftermarket scanners just won’t do. I have a Snap-On scanner, and the european software package is a joke.
Also, while you’re at that shop, have them look at the transmission adaptation data. Make sure the adaptations aren’t maxed out. The adaptation data will give the mechanics an excellent idea of the condition of the transmission.
Has the transmission fluid and filter ever been serviced? Only use the factory ATF. I recommend against a flush.

DO NOT use that generic multi-purpose one-size-fits-all ATF.

@barkydog the w/s switch does influence the shifting. It doesn’t make a huge difference one way or the other.

Did you put in the correct Bosch ignition wires. Again, sometimes the engine doesn’t like the “wrong” wires.



I’ve seen cars that actually had slight misfires BECAUSE of installing these.


I don’t know what plugs or ignition wires were used, I didn’t do the work, nor had any input on the matter.

I spoke with my stepdad a few minutes ago, and he said he turned the engine on and off about 5 times, and now the check engine light has gone out. However he didn’t drive it. I’ll see if I can swing by their place tomorrow after work and take the car out and see if I replicate the initial problems I experienced earlier today. Someone on another forum mention that the ring gear adaptation limit might also have been met and the ECU may be retarding the ignition timing. Any thoughts on that? I wouldn’t think it would effect the transmission, but it might explain why the engine seemed to be down on power.

That’s for your input, I’ll try to see what specific type of plugs and ignition wires were used. I don’t know the service history on the transmission though.

Sounds like a (not cheap) trip to a good MB tech is in order. Comes with the territory, unfortunately.

Sorry I’m a bit late on the update, but I didn’t get chance to drive the car again until today. I took the car out for 10 minute drive today, and it drove perfectly, Plenty of power and prompt downshifts. I did note some slight rattling from the engine at idle when observing the car from the outside, but inside the car you can’t hear it.

The ignition wires are apparently OEM from the MB parts counter, and the plugs are OEM Bosch as well.

2nd gear starts? Sounds like my Chevy power glide trans. I could not spin my posi rear end impala even in snow. Never, ever got stuck in that car. And I thought newer cars came with 5, 6, 7 speed trans for improved acceleration and fuel economy?

@Stoveguyy it has a 5-speed automatic transmission.
It is programmed to start in 2nd gear, unless the driver forces the downshift into 1st.

Wow, those Mercedes engineers sure are clever. I can see a wimpy clk320 with 2nd gear econo starts. But this is the V8 model. How about a little pep? I bet the car even has a driver selectable shift mode for sport-Econ-snow mode? I wonder if trac control can be shut off so u can do a burnout?

@Stoveguyy there is a w/s (winter/summer switch) and and ESP (electronic stability program) off switch.
I don’t know why you’d want to do burnouts in a 4 seat luxury convertible. Those aren’t the kind of customers that bought those cars.

“I don’t know why you’d want to do burnouts in a 4 seat luxury convertible. Those aren’t the kind of customers that bought those cars.”

Yeah, but then their kids get their hands on them.

ha ha

275 HP in a car that size isn;t going to scare any Aston Martins, but it does sound like the car is overdue for some TLC.

As regards the difference in performance, I suspect that originates in the difference in,shall we say… driving styles. But if it were mine I’d bring the car in and get it checked out. Oinging and CEL lights even under hard driving need to be looked at.

@db4690, a neighbor owns a CLK500. He used to drive it until he bought a new 750iL two years ago. Now one of his kids drives the Benz. And don’t forget his wife’s Escalade, his new Suburban, his F150 Harley Davidson, and whatever his kids are driving. Must be nice to be him!

@the same mountainbike

On Monday, my mom gave me a ride to go pick up my car that was getting a state inspection. I drove the car on the way to the shop doing the inspection, a journey of about 10 miles. Initially the car started and drove fine, there was no lack of power, and the transmission was shifting properly, about a mile from the shop we came to a red light and stopped, when the light turned green, I tried to accelerate, but the car balked momentarily, and then started accelerating quite slowly, gave the car full throttle to see if it would kick down to 1st gear, it did not downshift. when we reached the turn off to go the shop, again the car would accelerate like it had suddenly lost 150 HP, and the transmission again didn’t seem to want to downshift. However the check engine light did not come on this time. I told my mother what was happening, and she noticed the problem as well when she was driving the car back home. However yesterday she said that the car drove perfectly on her way to work, and then back home again after work. I told her that she needs to take it in to a MB shop to see what’s going on. If and when she does I’ll report back with their findings.

I realize that 275 HP isn’t going to be Ferrari territory, but this thing was so down on power than I think a Bluebird with 50 kids aboard would’ve shown the Benz its taillights.

@FoDaddy you might have a bad MAF

Thank you for an excellent feedback post.
Even though the CEL light is no longer on, it’s very possible that the computer has stored some fault codes that would suggest why the failures occurred. Db4690 might be right about the mass airflow sensor, however I’d expect a MAF failure to produce a more consistant symptomology.

Another possibility is a failing fuel pump. That can be tested for.

The transmission not shifting sounds to me to be a secondary effect of the intermittant power loss rather than a fault of its own. I think once you get the engine operation sorted out the tanny will work normally.

I’m looking forward to the shop’s finding.

Im late to the game but researching the 430 and found this. Wondering if it ever was figured out? I read through a lot of it and to me it kept pointing to the EPS or ESP (cant recall)button…I bought one of these (2001 clk 430 Cab)at an auction to keep at my vacation home in Az and the first day I kept hitting that button because it was where I thought the window button should be. It only reset if I turned off the car and restarted it. Easy fix but it scared the crap out of me that I wasted dough. Ive since sold it this last summer and now looking to buy another one here in Seattle for my sons first car (now that im familiar with them). This time doing my due diligence.