I am on my last limb trying to fix this problem in my 1990 740 GL. I have been chasing a rough idle / harsh start / suspected lean fuel condition for months now. I have replaced (including but not limited to) the spark plugs, the spark plug wires, the starter, the alternator (twice), the battery, the MAT (mass air temp because I’m running the Regina fuel system), and the o2 sensor. And it’s STILL THERE. I don’t know what to do at this point, I would appreciate any advice.