C209 CLK320 Safe Mode Problem

[Gitbags]

Morning all newbie to the Mercedes Scene here,
After years of driving Japanese Rocket ships i took the plunge into the realms of comfort and luxury and now have a 2003 CLK320(Petrol) which is proving to be a pain in the butt, everything is fine in regards to running etc until i hit between 70 and 80mph under gentle acceleration and the engine warning light comes on and the engine goes into limp home mode. If i accelerate hard then the problem doesn't occur!!
I've plugged it into a Code Reader to see what codes are stored and it shows P0300, P0301-2-4-5-6 etc. Only number 3 pot doesn't show the error code. The leads and plugs have been changed to eliminate faults that end. I know the codes show as random misfires and i suspect that at 109000 miles the coils may need changing but cannot see why they would only fail under gentle acceleration and not when flooring it.
The MAF has also been changed along with the fuel filter for OEM parts so don't think its fuel related leading to the ECU shutting down the affected cylinders.
I'm lost as to what to try next so any input or help would be appreciated. I am a qualified mechanic for both cars and bikes but this one has me puzzled.
Now its back to my man cave and the change over of the rear upper control arms to stop the damn squeaks.

Cheers

 

[IanW]

Not a great help to you, but I had a very similar problem about a month ago on my CLK500 - EML plus a varied assortment of P030X codes. After clearing the fault, it would re-appear consistently once RPM exceeded 4K. I replaced the MAF with another Bosch one; it had done 80+K miles, so it was due for renewal. Engine running improved, but would still occasionally light the EML and give a P030X code at high RPM. Measuring all the spark plug leads mostly showed 2K ohms, however some of them went open circuit when flexed, so I bit the bullet and bought a new set of 16.
At this point, there was just a slight misfire at idle. The iCarsoft code reader is able to read the 'smooth running' live data. this showed that cylinder 5 was causing the slight roughness. One new coil pack and the engine idle is perfect, 'smooth running' values are identical for all cylinders, and the engine pulls cleanly to the red line with no fault codes.
I'm just waiting for the crankshaft position sensor to fail now...
I'd start by checking the HT lead resistance, flexing them at the same time to check for intermittent faults. I'd also find a STAR or iCarsoft M-B specific reader to check the smooth running data - that proved far more reliable in finding the faulty cylinder than the generic OBD P030X codes.
Is your MAF a genuine Bosch one? I've never had a problem but others on this forum have had trouble with non-Bosch MAFs.

Good luck!
Ian.