Cross-posting here (was in performance) in case there are more people here -

I recently picked up a really nice '98 C43 AMG. Car has 98K. Runs perfectly except that if you really floor it, it throws a P0303. I swapped coil packs, stayed on cyl 3. I looked closer at the wires and found the shorter one wasn't clipping into the coil pack properly. I pulled it, repaired clip and moved that wire to cyl #1. Still firing the 303 code. Can a plug cause this or should I be looking at the harness? I wasn't at a place where I had the socket to pull the plug so I haven't seen it. However, I am thinking that if it's been doing this a long time, the plug is prob fouled.

Other symptoms - when the 303 get's tripped, the car idles terrible like a cyl isn't firing. Simply shutting the car off/restarting clears the rough idle condition. Does the computer have a way to lock out a cyl on misfire detection? Also, car high idles (about 1400 RPM) for a little bit on startup. I found a vacuum line off coming off the back of the manifold and it heads over towards the passenger side corner of the engine compartment then disappears, presumably into the car. Reconnecting it has had no affect.

Other than that, car runs beautifully and I am averaging 23MPG which I think is decent for this car.

Thoughts?

BTW - this is my first non-diesel mercedes so even 1/3 throttle is way more than I ever had before LOL, but I'd like to figure out what's going on.