Vintage Cars: 528e Uneven Idle / Speed, but no torque, premium fuel, 5th gear

Question
Hi Ron,  
I have a '84 528e.  The car is awesome.  Everything works except the instrument cluster.  (Which one day I'd like to get fixed.)  I keep Premium fuel in it and have replaced everything what was worn out or broken.

I commute 45 minutes everyday.  Recently I have started noticing a sharp decline in low end power.  I used to be able to accelerate while in 5th Gear on a highway. Now I have to shift down to 3rd at highway speeds to get any action.  If the car is on a flat surface it is OK, once you get it off the line.  It can't climb hills without a running start, which is a problem in San Francisco.  I took it to a place that specializes in BMWs, but I think this vintage was out of their expertise.  They charged me 300 bucks to tell me that they couldn't figure it out.

I read your post on the relay or ECU going bad.  Everything you said made sense.

The Fuel or Air deliver seems to be a problem.  At Idle, the engine shakes a bit in the engine bay. The RPM gauge still works and the needle dips about every 2 seconds.

Thinking it had something to do with the after market stereo or the previous owners cheap alarm system, which has been partially ripped out, I systematically removed all the fuses and started the car.  When I removed one of them (I think it was the instrument cluster) the car roared when it started and seemed really strong, but the idle seemed too high to attempt putting it in gear.

Does what I am describing along the same lines as a bad ECU or Relay?

What should I do to get this amazing car back in order?...And what should I spend?

Thank you,
Sean

Answer
well lack of power can be several things , but most likely it is related to fuel delivery and or air delivery.
I would rule out any fuel filter blockage as well as restricted injectors. have you changed filters recently?  Fuel pump pressure OK?  how many miles on the filters?   AIr intake clean, clear?  Have you tried running injector cleaner? How many miles on the car?
ECU controls lean rich mixture , and once running has only little influence on performance.
i am not sure what relay you speak of , other then fuel pump

Was this a sudden onset, after you did a service ?  or come on gradual.
More information you can give me the better.  I have a good friend that does BMWS, I will also ask his opinion