to make a long story as short as possible I picked up a 1999 CLK430 and had the MB dealer do the inspection everything came back fine. The car had the mass air sensor replaced about 4 months ago by the same dealer for the previous owner. About a week or two after I purchased it I noticed that when I punch the gas real hard the car was basically falling on its face and accelerating real slow with the RPM's at about 3500 rising very slowly. I took it to the a different MB dealer (where I live) and I had them service the tranny to be safe. It still ran bad when hitting the gas hard so I took it back again to the same dealer they ran some more test rest the adoptions and said the only thing that came back with any problems was the crankshaft positions sensor instead of paying another $300 to have them do it, I ordered it and replaced it myself a couple weeks later but since they had re-set everything it ran great for a week in between. Before I replaced the CPS I did a battery reset at my house instead of going back to the dealer and that fixed it for another week or so. Right before I actually did replace the CPS it started doing the same thing again. This time I took the car to a very well know independent MB mechanic called MBI here in Portland OR. They did all the test they could said all the adaptions where almost perfect but did say that the CPS had not been reset since I did it myself. They cleared the ME (Engine Electronic Control Module) to the initial factory settings. And of course the car runs perfect again. They said that if the problem comes back then they are pointing to-wards a new computer. They said I could get a used one and send it to Beckman Technologies in N. Carolina and they could unlock it for me. I called them and spoke to a gentlemen and he really doesn't think I have a bad computer he said these computers are always mis-diagnosed and they are a very reliable computer. So right now I'm stuck and really hoping the problem doesn't come back and something MBI did get fixed but if someone has any ideas as to what the problem could be please please help me out here. Oh yeah car runs perfect all the time if you don't punch the gas, I only know there is a problem when I step on it.
Thanks so much[/align]

 

Hi,
Driver symptoms suggest MAF.
However this gives a diagnostic signature so if no codes are set then it is unlikely the MAF.

IMHO the engine computer is as robust as these things can be and after X years and miles the chances of it being faulty reduces unless it has got wet.

So I suspect that something is wrong somewhere in the data you have been provided with.
People talk about "Adaptations" but this is just a fancy word for an offset which is determined by engine/trans usage. The car learns wether you are a steady economical driver or one that uses the available HP regularly by measuring Short Term Fuel Trim (O2 sensor feedback vs "ideal" mixture). This value is then applies as offset to the fueling map in order to try to lean the engine out as much as is consistent with your driving style. STFT values are "averaged" by some process that generates a LTFT which is a base offset that is applied when the engine is first started and remains valid until the next start.

I still think that the MAF in your car MAY BE wrong. Could it be a cheapo replacement (eBay / China copy etc) or alternatively the wrong model or a diesel in lieu of gasoline. Ensure it is a genuine bosch sehsor (not housing) and of course the correct number.

However I'm still surprised by no codes.
So what "adaptation" values were actually measured.
These values are "lost" after a reset.
I know them as Long and Short term fuel trim LTFT/STFT.
LTFT above 30 gives a problem.

CPS gives restart problems when hot, but since this has been changed and you don't have hot or cold start problems.
(I wasn't aware that anything needed to be reset since the CPS doesn't normally set a code, since it is checked at Startup and will be found to be OK. It fails due to under hood high ambient temp. i.e. It recovers once the temp drops.)