My kingdom for a competent diagnostician!!!

[craig from iowa]

If I could find one, I sure wouldn't have to post questions here (although the advice is top-notch, and I visit this site daily).

I have a 97 e320 with 115K miles. My problem is with just ONE spark plug that continues to foul (#5 plug). I have changed the spark plugs (now using the recommended Bosch FDC4), spark plug wires, coils, the connectors between the coils and the plugs, crankshaft position sensor, mass air flow sensor, and both oxygen sensors. I didn't mind putting all of these new parts on due to high number of miles already on the car, and I do get some jollies tinkering around with engines. After doing all of this, the aforementioned #5 plug continues to foul, although the check engine light is no longer on, and the performance (and idle) is somewhat better.

When I first start the engine in the morning, the idle is not steady. It seems to 'surge' and 'unsurge' until it gets up to operating temperature. The problem is most pronounced when I first shift the transmission into reverse from park. If I continue to hold the brake pedal down (have to have it pressed in order to shift into reverse), the engine lurks and spasms and acts like a wild horse that is being domesticated.

As mentioned in the title, if I could find a good technician in my area, I'd take it there and let them fix it. However, I've had this car to a competent indie, as well as to an authorized MB dealer. At least the indie was honest when he said 'I just can't find what's wrong with this car'. The MB shop just switched out the MAF and said 'Ok, your car is fixed. Come pick it up, and btw, please fork over $1,100 (new MAF and by inference, 10 hours of diagnostic time).

It certainly has been a frustrating experience trying to get this problem fixed. The car still looks new both inside and out, and I love driving it, especially out on the highway where I can set the cruise at 85 mph. No highway troopers in Iowa due to budget cuts....jk. The car almost drives itself.

Any ideas on what could be causing that #5 plug to foul?

Thanks in advance.....I like this site the best out of the 3 MB forums I read.