I am going out of my mind with a misfire. It's a 1995 E320 with 120,000 miles on it. A few weeks ago the car began to run roughly just once when I ran over a few bumps, kind of like a misfire. No CEL illuminated, the problem resolved within three-minutes. A few weeks after that without warning, it happened again for the second time. The same thing happened, a few minutes later it resolved. Now this misfire is permanent. The wiring harness was bought brand new three-years ago. The spark plugs are all Bosch F8DC4. The ignition coils were all proactively replaced along with the rubber plug boots three-years ago. The only code I ever get is #23, "ignition misfire/coil with cylinders 3 & 4". I have replaced the coil over number 4 with three known good ones, I have replaced the plug wire and boot that leads to plug number 3. I just tried replacing both spark plugs for cylinders 3 & 4 with brand new Bosch F8DC4 plugs. It's always the same, the car shakes violently, the exhaust smells awful (obviously raw fuel is escaping), the shaking is worse in R or D. The code is ALWAYS the same, #23. I did an extensive search on this very common problem. Usually by replacing the coil or switching to the correct plugs solves everything. There is no gas in the fuel regulator vacuum line, I disconnected the MOT valve briefly, no change. I cleaned the MAF sensor with CRC-brand MAF sensor cleaner. The rough idle is instant when the engine is started as is the code (#23). WHAT IS WRONG WITH THIS?

The OVP has been replaced (two-years ago) with the MB-brand, the 15 amp fuse is still intact. When swapping the coils, the fault does NOT follow the coil. I just swapped two of them, I still get code #23, cylinders 3 & 4.

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