I know the vacuum hose you are talking about and we checked and re-checked it. It was not knocked off.
I got a call from the dealer service advisor just before dinner, and the car is ready to be picked up.
They replaced the intake manifold gasket, and it fixed the problem.
The technician drove it extensively at operating temperature, and the fluctuating idle didn't reapper.
He also hooked it up to the scanner, and there were no more codes.
I have no idea why the gasket went bad, particularly immediately after the water pump replacement. I guess it's one of those strange coincidences.
I'm just glad it's fixed.
Again, I feel like everytime my car exhibits a problem, it's not the normal solution. My mechanic spent a whole day working on the car, and couldn't positively diagnose it.
Once more, I feel like Charlie Brown in the Peanuts Halloween special. The gang goes trick or treating, and after receiving the 'treat', they all compare what they got. One says "I got an apple". Another, "I got a candy bar!", and so on. Charlie Brown says "I got a rock!".
I feel like my car has been a "rock". I hope it gives me at least 6 months of relatively trouble free service...
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".