its obvious from your comments that you don't have the "feel" part of it - you seem to be just like some of the people I have met who cannot think unless they have 8 different gadgets read them some output. No wonder this is what happens when you go to most dealers - they'll blabber some tech stuff and rip you out of a couple of grand, without diagnosing or understanding the real problem, which is often solvable in a couple of hundred bucks. And don't tell me that doesn't happen - I can quote you many many instances where it HAS happened. And by no means do I mean to offend the honest guys out there - I myself know one of those, so whenever feasible, I am willing to drive 500 miles to show him the car instead of the local dealer!
Anyway, thanks everyone for those who provided me some useful pointers, and there are many of those in the responses above, Jim, which you may like to learn finally.
BTW, what IS high fuel consumption? There's obviously a normal operating range for every car, but when should one get alarmed? You can't just to go a techy everytime you feel something MIGHT be wrong - is 19 mpg city driving abnormal enough to deserve diagnosis in a 85 190E 2.3, 113K miles? Nobody seems to have addressed this issue. Excuse me if this issue is not "Techy" enough, but isn't it extremely important and useful for EVERYONE who owns this car?