My car oil pressure is low and it's vibrating in drive?

I have a 1984 Mercedes 190E automatic with about 128,000 miles on it. The oil pressure guage rates the pressure from 0-3. Normally it's on 2(in drive) and somewhere from 2-3(in neutral/park). For some reason it's dropping to 1 or 1.5 (in drive and neutral). In drive it vibrates a lot, not too much in neutral. I already checked the dip stick and i have enough oil. I chaged the oil last week thinking that was causing the problem, but it's still vibrating. We also tried to adjust the throttle cable but no luck with that. Air filter and plugs were also changed recently. Any suggestions?My car oil pressure is low and it's vibrating in drive?
Even though you have enough oil, or if the oil is clean, it's a strong possibility that the Oil Pump is malfunctioning. You can have all the oil in the world, in the engine of your car; but it wouldn't do you any good if the oil pump is not working to lubricate the engine parts while they're rotating. It sounds like you have a faulty Oil Pump. Have it replaced as soon as possible to avoid costly engine damage. Unfortunately though, the Oil Pump is located within the Oil Pan. To get to it; the mechanic has to do one of two things. Either raise the engine off the engine mounts or remove a portion of the front suspension because it's blocking it. In either case, your looking at between 3-5 hours of labor time, plus an additional hour of labor to reinstall a new pump. If a typical Mercedes dealer charges over $100 an hour, your looking at around $700 in labor charges and possibly $300 for a new pump. But, if you leave it alone, you end up destroying your engine; and a new engine with labor time is probably around $10,000. So do the math. Either spend $1,000 now; or $10,000 later.My car oil pressure is low and it's vibrating in drive?
Check the wire on the oil pressure switch. It sounds like the wire has a loose connection. And check the connections on and around the alternator.It just sounds like a loose ground wire !
The 190E was notorious for head gasket failure. I'd do a compression test and if that's okay, a pressure test on the cooling system to see if coolant is diluting the oil and or fouling one or more spark plugs.