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The high fuel consumption and smoke would seem to indicate the fuel/air ratio is incorrect. Along with the surging problem, I'd tend to think along the lines of a bad throttle motor assembly, but this is just a guess. A fairly common problem could be a mass airflow sensor. Doesn't really sound like the OVP to me, but maybe the people you are talking to have seen these symptoms with a bad OVP and I haven't. Possible I suppose. If you can find the OVP (I am unsure of the location of it on this model, but I'd start in the area of the right rear corner of the underhood area) you can check the fuse on top of the relay.
Very unusual no code situation (no warning light) if the problem would be either the throttle motor or MAF.
possibly check the rubber "elbows" where the air flow enters the intake manifold to make sure they are tight and no cracks in the rubber.
One thing you can try is pulling off individual spark plug boots (just one or two on each side) to see if it affects operation of the engine. This way you can be sure that both banks are operating. The engine will actually idle pretty good on just one bank, but of course you expect BOTH banks to be operating. If pulling plugs on one side of the engine affects the idle, and not the other, then you know you have a bank shut down. There are individua control systems for each side of the M120 motor, it kind of operates like 2 inline 6's. Like 2 M104 engines to be exact.
Gilly
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